Impact of gargling on respiratory infections

Abstract

Respiratory infection is one of the leading causes of death in the world. The outbreaks of influenza and the Middle East respiratory syndrome have added to the miseries of human beings. Interventions such as the use of masks, social distancing, hand washing, and the use of personal protective equipment by health care professionals have minimized the transmission of pathogens from infected to healthy individuals. Another intervention is gargling which is most commonly performed by the Japanese to avoid respiratory infections. PubMed was used to search articles on gargling in respiratory infections published in the last three decades. Gargling is effective in upper respiratory infections (URTIs). URTI precedes lower respiratory tract infection; early intervention could prevent complications. The gargling agents in this review are classified as synthetic and natural gargling agents. The mouthwashes or gargling agents reviewed in this article have proven efficacy in reducing either bacterial or viral (or both) respiratory infections. The mouthwashes available over the counter may also have side effects. The use of mouthwash should be based on the potential benefit of oral and systemic conditions.

KEYWORDS:

• Respiratory infections
• gargling
• synthetic agents
• natural agents
• and mouth wash

Introduction

Lower respiratory infections (LRTIs) are one of the leading causes of death in the world. In 2016, the estimated deaths due to LRTIs were 652,752 affecting mostly children under the age of 5 years and elderly over the age of 70 years (Troeger et al. 2018). Millions of dollars are spent on the management of the LRTIs annually. Deaths due to LRTI caused by influenza were about 145,000 in 2017. Increased numbers of hospitalization days have been reported due to LRTIs caused by influenza (Troeger et al. 2019). Acute respiratory infection caused by viruses from the corona family can also develop respiratory complications. The Middle East respiratory syndrome (MERS) may progress to respiratory failure while the complications of severe acute respiratory syndrome are less severe as compared to MERS. Human coronaviruses may also cause pneumonia but of less intensity (Yin and Wunderink 2018). Similarly, the influenza virus can also cause pneumonia and resulting in morbidity and mortality (Rothberg et al. 2008).

In any pandemic and epidemic, respiratory infections physical interventions can be useful. Exposure to airborne pathogens poses a threat to human life which needs mitigation through physical interventions. These physical interventions include physical distancing (social distancing and isolation of infected individuals), barriers, and personal hygiene. Barriers include the use of masks for the general public, infective population, and health care workers. Goggles, gowns, and gloves for health care workers. Personal hygiene involves handwashing (Jefferson et al. 2008).

Apart from these interventions, another technique is gargling which can be prophylactically used to prevent as well as reduce complications of respiratory infections. Gargling can be effective in the management of upper repertory infections (URTIs) as well as a cost-effective and safe technique. It reduces the burden on the health system (Sakai et al. 2008). A cross-sectional online survey in Japan has demonstrated that physical interventions including gargling can be useful in avoiding influenza (Takahashi et al. 2017).

The commercially available mouthwashes for gargling are divided into two types: cosmetic and therapeutic mouthwash. Cosmetic mouthwashes are used to get rid of bad breath and a pleasant taste is left behind. The therapeutic mouthwashes are available both on prescription and over the counter. The therapeutic mouthwashes are mostly used for dental problems and oral infections (American Dental Association 2019, August 29).

Gargling cannot treat LRTIs effectively. URTI precedes LRTI; early treatment of URTI can prevent complications of LRTI. The recommended gargling time is 30–60 s and should be adequately used so that it may reach the parts of the oral cavity where the pathogens are present (Phillips et al. 2020). The proposed mechanism of action and antimicrobial activity of synthetic agents and natural agents used for gargling are described in Tables 1 and 2, respectively. Japanese lifestyle includes gargling in their routine life. More clinical trials have been conducted in the Japanese population than any other ethnic group.

Table 1. Mechanism of action, antimicrobial, and antiviral activity of mouthwashes from synthetic origin.

Mouth wash type	Mechanism	Activity against microbes and viruses
Povidone Iodine	Effectiveness is due to the conversion of iodide to molecular iodine (I2) and hypoiodous acid (HOI). The two forms of iodine disrupt the cell walls of microbes by inducing pore formation causing loss of cytosol and enzyme denaturation (Eggers 2019).	Gram-positive bacteria, Gram-negative bacteria, mycobacteria, fungi, chlamydiae, viruses, and protozoans (Schreier et al. 1997).
Chlorhexidine	Low concentrations: bacteriostatic and cell irreversibly damaged. Higher concentrations: bactericidal by causing the precipitation of cytoplasm (Basrani 2005).	Gram-positive and Gram-negative bacteria. Facultative anaerobic and aerobic bacteria, spores, viruses, and yeast (Basrani 2005).
Benzydamine	Synergize the effect of antibiotics. Increases bacterial uptake of tetracyclines and chloramphenicol (Quane et al. 1998)	Nonspecific antibacterial activity (Quane et al. 1998)
Cetylpyridinium Chloride	The positively charged cetylpyridinium chloride is attracted by the negative surface of the bacteria and adsorption on the cell causes the death of bacterial cells (Franklin et al. 2014)	Candida albicans (Fu et al. 2014), Actinomyces, Campyaobacter, Moraxella, Veillonella, Eikenella corrodens, Porphyromonas gingivalis, Prevotella intermedia, and Prevotella nigrescens (Sreenivasan et al. 2013)
C31 G	The alkyl portion of C31 G disrupts the microbial membrane (Corner et al. 1988).	Gram-positive bacteria, gram-negative bacteria and Candida albicans, yeast (Corner et al. 1988), Influenza A and influenza B virus (Lee et al. 2014)

Table 2. Mechanism of action, antimicrobial, and antiviral activity of mouthwashes from natural origin.

Mouth wash type	Mechanism	Activity against microbes and viruses
Sodium chloride	Intracellular hypochlorous acid (HOCl) has antibacterial and antiviral activity. By increasing the availability of sodium chloride (hypertonic solution) in non-myeloid cells can enhance the formation of HOCl.	A broad range of bacteria and viruses (Block and Rowan 2020). Herpes simplex virus-1, murine gammaherpesvirus 68, respiratory syncytial virus, influenza A virus, human coronavirus 229E, coxsackievirus B3 (Ramalingam et al. 2018).
Green tea	Green tea extracts inhibit influenza infectivity by preventing the entry of the virus into the cells. Inhibits virus growth by preventing acid-catalyzed fusion reaction and thus inhibits the growth of influenza A and B (Imanishi et al. 2002). Antibacterial activity by (i) cell wall and cell membrane disruption; (ii) inhibition of intracellular enzymes; (iii) oxidative stress; (iv) DNA damage; and (v) iron chelation (Renzetti et al. 2020)	Antibacterial (methicillin-resistant Staphylococcus aureus or Stenotrophomonas maltophilia, Aggregatibacter actinomycetmcomitans, Vibrio cholera, Lysteria monocytogenes, Pseudomonas aeruginosa, Escherichia coli, Clostridium perfringens, Bacillus subtilis, Staphylococcus epidermidis, Acinetobacter baumannii, Stenotrophomonas maltophilia, Pseudomonas fluorescens, Mycobacterium tuberculosis, Actinomyces, Bordetella bronchiseptica, Serratia marcescens, Salmonella enteritidis, Proteus mirabilis), antifungal (Candida albicans), antiviral (influenza virus) (Renzetti et al. 2020; Steinmann et al. 2013)
Essential oils	The proposed antibacterial mechanism of essential oils is the disruption of the cell wall of bacteria and inhibition of bacterial enzymes. It is also assumed that the essential oils extract the polysaccharide-derived endotoxin from gram-negative bacteria (Mandel 1994).	Herpes simplex type-1 and type-2 and influenza A, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus vulgaris, Bacillus subtilis, Staphylococcus aureus Streptococcus mutans, Enterococcus faecalis,Eikenella corrodens and Candida albicans (Dennison et al. 1995) (Prabuseenivasan et al. 2006; Serra et al. 2018; Vlachojannis et al. 2015)
Licorice	Wang, Yang et al., has described the antibacterial, antifungal, and antiviral mechanisms and activities in detail (Wang et al. 2015).	Human respiratory syncytial virus, Herpes simplex virus, Methicillin-resistant Staphylococcus aureus, Methicillin-sensitive Staphylococcus aureus (Wang et al. 2015), influenza A virus (Wolkerstorfer et al. 2009),Streptococcus pyogenes, Haemophilus irnfluenzae and Moraxella catarrhalis (Tanaka et al. 2001)
Eucalyptol	(Eucalyptol) 1,8- cineole suppresses mucus hypersecretion caused by rhinosinusitis and bacteria (Cai et al. 2020).	Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli and Candida albicans, and biofilm cultures of MRSA and Pseudomonas aeruginosa. (it is more effective when used in combination with other essential oils and antiseptics) (Hendry et al. 2009)
Lactoferrin	Lactoferrin act as a bactericidal by interacting with (i) lipopolysaccharide of gram-negative bacteria or (ii) by the interaction of lipoteichoic acid of gram-positive bacteria. Lactoferrin has virucidal activity by blocking cellular receptors or by direct binding to the virus (Berlutti et al. 2011)	E. coli, Staphylococcus aureus, Pseudomonas aeruginosa, Helicobacter pylori, Bacillus subtilis, Vibrio cholerae, and Candida albicans. Cytomegalovirus, HIV, Herpes virus, Hepatitis B and C, Hantavirus, Human papillomavirus, Rotavirus, Adenovirus, and Influenza A (Hill and Newburg 2015)

In this article, studies conducted on gargling and its impacts on respiratory infections are reviewed.

Methodology

PubMed was used to search articles published in the last three decades on gargling in respiratory infections. The following keywords were used in the search: ‘mouth wash’, ‘mouth rinse’ and ‘gargling’ in respiratory infections. During collecting the data it was observed that two main types of gargling agents are used i.e. synthetic origin and natural origin. The synthetic agents in this review article include; Polyvinylpyrrolidone–iodine, chlorhexidine, cetylpyridinium chloride, benzydamine, ketamine, sodium azulene sulfonate, ketoprofen, nystatin, and furaginum. Gargling solutions from natural sources included in this article are; sodium chloride, tape water, green tea, essential oils (Eucalyptol), licorice, and bovine lactoferrin. Case reports were not included in this study. Articles on ventilator-associated pneumonia were excluded as a plethora of research articles and review articles are available on the subject.

Gargling in respiratory infections with synthetic agents

Polyvinylpyrrolidone–iodine

PVP-I mouth wash product has both virucidal and bactericidal in vitro activity against the pathogens found in the respiratory tract. PVP-I 0.7% and 0.23% solution reduced the bacterial count by 99% of Klebsiella pneumoniae and Streptococcus pneumoniae. 0.23% PVP-I solution proved to be virucidal against Influenza virus A subtype H1N1, severe acute respiratory syndrome coronavirus (SARS-CoV), MERS CoV, and non-enveloped human rotavirus strain(Eggers et al. 2018). The MERS-CoV is a type of coronaviruses. PVP-I 1% mouth wash solution has proved its effectiveness within 15 s during in vitro studies against MERS-CoV (Eggers et al. 2015). Other in vitro studies have demonstrated that Iodine and Chlorine fresh solutions are effective against enveloped viruses while quaternary ammonium compounds were effective against non-enveloped viruses (Shirai et al. 2000). 0.23% PVP-I gargle solution and 0.23% PVP-I throat spray diminished three strains of avian influenza in 10 s during in vitro experiments(Ito et al. 2006). A study revealed that PVP-I gargles are effective against bacterial URTI caused by Pseudomonas aeruginosa, Staphylococcus aureus, and Haemophilus influenzae. (Nagatake et al. 2002). This study is not reliable because control was not used and it was not a randomized controlled trial. Further in vivo studies are required to confirm the antibacterial activity of PVP-I gargle. Bordetella pertussis causes pertussis which is an acute respiratory tract infection. In vitro studies demonstrated that PVP-I gargle solution (0.05%) was effective against the Bordetella pertussis whereas benzethonium chloride gargle solution (0.2%) had non-significant bactericidal activity (Suzuki et al. 2012).

An in vitro and in vivo bactericidal activity was conducted in Japan to compare the effect of PVP-I, chlorhexidine gluconate, and cetylpyridinium chloride. PVP-I was effective against the bacteria both in vitro and in vivo in the comparative study. The incidence of influenza and common cold were significantly reduced in the groups in which PVP-I was used for gargling. Cetylpyridinium was effective as compared to chlorhexidine. The lack of chlorhexidine antibacterial activity and ineffectiveness against influenza and common cold may be due to the low concentration. Chlorhexidine mouthwash is not recommended in high concentration or undiluted form because of its side effects (Shiraishi and Nakagawa 2002). Gargling twice with 2.5 mg/ml PVP-I before surgery reduces the number of microorganisms and bacteria in the upper respiratory tract (Ogata et al. 2004) Aspiration pneumonia is very common in elderly people. Special care is required in elderly people to avoid respiratory infections. A study was conducted in nursing homes to evaluate and compare the effects of oral health care by dental hygienists with PVP-I gargling. The PVP-I gargling proved to be less effective as compared to oral health care in elderly people. (Ishikawa et al. 2008).

The Iodine in PVP-I may induce hypothyroidism with continuous gargling which resolves after discontinuing the gargling (Sato et al. 2007). In vitro studies and animal studies have demonstrated that PVP-I causes apoptosis and necrosis (Sato et al. 2014).

Chlorhexidine

In vitro study demonstrated that Chlorhexidine (0.12%) has virucidal against enveloped viruses such as Herpes simplex, Cytomegalovirus, hepatitis B, Influenza A, and Parainfluenza viruses. The inactivation of the viruses was not uniform and dependent on time. Parainfluenza and cytomegalovirus took more time to be inactivated by chlorhexidine (Bernstein et al. 1990). Chlorhexidine (0.12%) and benzydamine (0.15%) mouth spray four times per day has proven to be effective in alleviating the symptoms of streptococcal tonsillopharyngitis along with the administration of antibiotics. The spray has mild side effects but relieves the local inflammation and pain thus improve the swallowing capability of the patients (Cingi et al. 2011).

A randomized controlled trial on patients aged ≥65 years was conducted to compare the efficacy of thymol gargles with chlorhexidine gargles. Once-daily gargling with chlorhexidine has proven to be effective as compared to the thymol gargling. The author described that the number of pathogens (microorganism) colonization was significantly reduced after seven days of chlorhexidine gargling. However, the nature of the microorganism has not been described (Sharif-Abdullah et al. 2016). A double-blind study on a fixed-dose combination of chlorhexidine and benzydamine spray relieved pain and symptoms of viral pharyngitis. The spray was self-administered four times a day with co-administration of 500 mg paracetamol (Cingi et al. 2010). Incidence of nosocomial pneumonia was evaluated by using 0.01% potassium permanganate as a control for oral cleaning in critically ill patients while chlorhexidine 0.2% was the test solution. Chlorhexidine did not prove to be superior as compared to potassium permanganate. Potassium permanganate has also some anti-pathogenic activity (Panchabhai et al. 2009). One study concluded that 15 ml gargling with 0.12% chlorhexidine three times daily does not prevent respiratory infections in conscious patients in intensive care units. However, the use of 0.12% chlorhexidine delayed the onset of the infections (Bellissimo-Rodrigues et al. 2009). Other researchers believe that 0.2% must be used to reduce the incidence of nosocomial infections (Panchabhai and Dangayach 2010). The incidence of pneumonia was reduced in nursing home residents who were aged above 65 years by using oral rinse with chlorhexidine (0.12%) along with manual brushing and upright feeding position (Quagliarello et al. 2009). Three techniques i.e. tooth brushing, tongue cleaning with a sponge brush, and wiping oral mucus membrane with chlorhexidine were evaluated, in aged dependent persons. Chlorhexidine wiping significantly removed the opportunistic pathogens in the pharynx. Not only tooth brushing but chlorhexidine wiping is also suggested for elderly people in whom pathogens causing infections are detected (Tashiro et al. 2012).

Common adverse effects of chlorhexidine observed in diabetic patients are taste changes and oral stains. Other side effects include the sore mouth and (or) throat, tongue tip irritation, and shortness of breath (McCoy et al. 2008).

Cetylpyridinium chloride

Cetylpyridinium chloride is a quaternary ammonium compound. The twice-daily use of 0.05% Cetylpyridinium chloride for 6 weeks has shown that it neither affects the normal oral flora nor promotes the establishment of non-oral and potentially pathogenic bacteria in the mouth (Radford et al. 1997). A randomized controlled clinical trial in healthy adults (18–45 years) was conducted on a spray containing cetylpyridinium chloride, glycerin, and xanthan gum. The spray effectively reduced the severity of symptoms of the upper respiratory infection. The frequency of the URTIs was also reduced (Mukherjee et al. 2017).

Side effects of cetylpyridinium include staining of teeth and tongue (not important from a medical point of view but is a cosmetic problem), ulcerations, and burning sensation (Haps et al. 2008).

Benzydamine

Benzydamine and aspirin gargles were compared for their healing properties of sore throat in patients undergoing elective modified radical mastectomy aged between 16–65 years. The patients were divided into three groups who gargled with 350 mg aspirin, 0.15% benzydamine (both aspirin and benzydamine were diluted up to 30 ml with distilled water), and control (mineral water) just 5 min before induction of anesthesia. Benzydamine hydrochloride gargles proved to be effective for 24 h while aspirin for 2 h in the postoperative sore throat (Agarwal et al. 2006). Benzydamine mouth wash is having a good effect on oral health but can be used as a psychoactive agent for recreational purposes (Robinson and Scully 2016). No other serious side effects have been reported except the tingling effect when benzydamine used in combination with cetylpyridinium (Herrera et al. 2005).

Ketamine

Ketamine gargle has been also found to be effective in postoperative sore throat in a double-blind study (Chan et al. 2010). Ketamine reduced the incidence and severity of postoperative sore throat in a single-blind study. Ketamine gargling was performed 5 min before elective surgery for septorhinoplasty under general anesthesia. The control group gargled with 30 ml saline and the ketamine group gargled with 30 ml saline containing 40 mg ketamine (Canbay et al. 2008). Ketamine mouth wash has shown no adverse effects in an open-label study (Shillingburg et al. 2016).

Sodium azulene sulfonate

Sodium azulene sulfonate has anti-inflammatory properties and is used to treat gastritis and ulcers. Patients undergoing surgery used 4 mg of azulene dissolved in 100 ml water for gargling. The azulene gargles significantly reduced the incidence of postoperative sore throat as compared to tap water gargling. However, this study did not describe the frequency, volume of gargle solution, and time required for gargling (Ogata et al. 2005).

Ketoprofen

Ketoprofen lysine salt mouth wash was more effective in sore throat treatment as compared to benzydamine hydrochloride in a single-blinded study (patients were blinded). The study was more focused on pain management rather than on infection control (Passàli 2001). Patients sensitive to ketoprofen may experience intraoral itching and edema of lips (Liccardi et al. 2003).

Nystatin

Nystatin 1% mouth solution has been effective in the prophylaxis of invasive pulmonary fungal infection in patients with malignancies. The Nystatin 1% mouth was gargled for 15 min after meals and before going to bed. However, normal saline and sodium bicarbonate failed to prove its prophylactic effectiveness in managing invasive pulmonary fungal infection as compared to 1% nystatin (Hu et al. 2013). Some of the commercial nystatin suspension contains sugar which increases the probability of caries (Scheibler et al. 2017).

Furaginum

Gargling of furaginum has been effective in acute tonsillopharyngitis when used in combination with systemic administration of antibiotics (Nosulya et al. 2015).

Gargling in respiratory infections with natural agents

Tap water

A Japanese study was conducted on individuals who were more prone to upper respiratory tract infections and did not gargle in routine life. In this study, tap water gargles were found to be more effective by reducing the incidence of upper respiratory tract infection by 36% as compared to PVP-I gargle. The subjects in the Japanese study, gargled with 20 ml tap water for 15 s three times consecutively (total 60 ml) and observing the pattern three times a day. The impact maybe because of the presence of chlorine in tap water in Japan (Satomura et al. 2005). A 2 × 2 factorial randomized control trial was conducted in Canadian University students. The students were randomized into four treatment arms; (1) vitamin D₃ and gargling, (2) vitamin D₃ and no gargling, (3) placebo and gargling, or (4) placebo and no gargling. Gargling was performed with 30 ml tap water for 30 s twice daily while the individuals in the vitamin D₃ arm were asked to take one capsule of vitamin D₃ weekly for two months (10,000 IU of vitamin D₃). Vitamin D₃ was found to be moderately useful for reducing the risk of URTI while gargling with tap water did not reduce the URTI in contrast to the Japanese study (Goodall et al. 2014).

A trial was conducted in the Japanese population, to evaluate the effect of tap water gargling on influenza-like illness. The Influenza-like illness was not prevented by gargling with tap water (Kitamura et al. 2007).

Sodium chloride

A mechanism has been proposed that sodium chloride (NaCl) can kill all types of viruses. The epithelial, fibroblasts, and hepatic cells have innate immunity and convert chlorine of NaCl to hypochlorous acid (HOCl). Hypertonic saline nasal irrigation solution reduced the incidence of upper respiratory infection by 1.9 days, reduced the consumption of the over the counter medication by 36%, within house transmission was reduced by 35%, and the virus shedding was also significantly reduced (Ramalingam et al. 2019).

1% solution of sea salt spray and lozenges which contained 8.75 mg flurbiprofen was effective in the prevention of post-operative sore throats as compared to a mouth wash which contained xylitol. The non-effectiveness of the gargles has been attributed that the gargles are expelled from the mouth leaving behind a small amount of their active ingredient as compared to the lozenges or spray (Aydın et al. 2014). The other possible reason for its non-effectiveness may be due to the nature of the active ingredients of the mouthwash.

Isotonic nasal wash (seawater) has proven to be effective in school-going children. 390 children were divided into two groups, standard treatment group (which included medications for the treatment of rhinitis) and standard treatment group along with saline wash. The isotonic saline nasal wash was much more efficacious resulting in alleviation of symptoms, reducing the use of medicines, and improved health status in common cold and flu. After acute illness, the isotonic nasal wash also reduced the episodes of URTI as compared to a control group. Isotonic nasal wash was applied in different ways of which fine spray i.e. milder cleansing strength showed higher acceptance by the children (Šlapak et al. 2008). In another study in Sweden, participants were young adults who were eligible for army service. The study was a cross over design. The period during which physiological saline spray was used showed reduced; duration, symptoms of URTI, nasal symptoms, medicine consumption including antibiotics, and the duties were less affected as compared to the period during which the saline spray was not used (Tano and Tano 2004).

Green tea

The main components of green tea are catechins and theanine. A meta-analysis that included five studies all of which were conducted in the Japanese population demonstrated that green tea and green tea extracts gargling is effective in the prevention of influenza (Ide et al. 2016). Observational studies showed that consuming green tea reduces the incidence of influenza. Capsules containing L-theanine and epigallocatechin gallate (equivalent to 10 cups of green tea) reduced the symptoms of influenza by 32% as compared to placebo (Furushima et al. 2018). The use of tea extract has been reported to improve immunity and alleviate the symptoms of influenza and URTI. In a randomized controlled trial in health care workers aged over 20 years, catechin (378 mg) and theanine (210 mg) 6 capsules were administered per day. The findings of the study were that catechin and theanine can be effectively used for the management of influenza symptoms (Matsumoto et al. 2011).

An observational study in schoolchildren aged between 2 and 6 years was conducted to evaluate the effect of different gargling agents on the incidence of fever linked to influenza and the common cold. Four gargling agents that included tap water, saline water, green tea, and functional water (alkali ion water or ozone water) were compared with the control group i.e. non-gargling group. Among all these agents, green tea proved to be more effective in reducing the risk of LRTIs (Noda et al. 2012). Another clinical prospective study was conducted in elderly people in a nursing home with the age of 83 ± 8.2 years (minimum 65 years age) using green tea catechin extracts for gargling. The elderly people performed gargling three times daily for three months and catechin tea extract (200 µg/ml) was found to be more effective than the control which was without catechin extract (Yamada et al. 2006). Another study conducted on a relatively young and healthy population (20–65 years) who were already vaccinated against influenza showed no significant effect of tea catechin gargling (400 µg/ml). The incidence of influenza and upper respiratory infection was almost the same in the catechin group and control group. The author has attributed the effect to the vaccination, age group, and immune response of the study subjects. Immunosuppressed elderly people, children, and non-vaccinated individuals are more prone to infection (Yamada et al. 2007). In another study, the gargling of green tea has no advantage over gargling with tap water in alleviating symptoms of influenza (Ide et al. 2014).

Aroma gargling has also proven to be effective in preventing sore throat and halitosis in a limited number of patients who underwent spine surgery. Aroma gargle solution is composed of peppermint, tea tree, and lemon oils in the ratio of 1:2:2, respectively. The components of aroma have antiviral, antibacterial, and anti-inflammatory activity (Oh et al. 2017). Catechins have negligible systemic availability and have minimal side effects.

Essential oils

Essential oils are effective against the bacteria in oral cavity. Essential oils as herbal products have demonstrated their activity against 40 different species of bacteria. The in vitro study was performed on 40 oral bacteria at the concentration range of 1–512 micrograms per milliliter (Haffajee et al. 2008). The essential oils were used in a randomized clinical trial on human subjects with a history of clinically recurrent Herpes labialis. The essential oils reduced the viral contamination for 30 min (Meiller et al. 2005). A review on the use of essential oils as mouth rinse has concluded that mouth rinsing products containing essential oils along with tooth brushing can improve oral health and hence reduce the incidence of respiratory infections (Alshehri 2018). In vitro studies have revealed that essential oils are effective against enveloped viruses (Dennison et al. 1995). Local or systemic allergic reactions may occur with the use of mouthwashes containing essential oils (Vlachojannis et al. 2013).

Licorice

In a study, licorice gargles were used in patients undergoing surgery and the subjects were not blinded. 0.5 gram licorice was dissolved in 30 ml water and the patients gargled for 30 s before the induction of anesthesia. The licorice gargles were effective in the management of postoperative sore throat (Agarwal et al. 2009). The efficacy of licorice gargle has been confirmed by a double-blind study in which it was more efficacious as compared to sugar solution gargles (Ruetzler et al. 2013). The effectiveness of licorice is concentration-dependent. Different concentrations of licorice gargling solution demonstrated that 1 gram licorice when dissolved in 30 ml of water, was effective than 0.25 and 0.5 gram of licorice in the post-operative sore throat (Honarmand et al. 2016). Glycyrrhizin an active component of licorice roots which is a potent inhibitor of SARS-associated coronaviruses replication in Vero cells (Cinatl et al. 2003). Licorice has several active compounds. Oral ingestion of licorice results in minimal side effects but its use in pregnancy is not safe (Nazari et al. 2017).

Eucalyptol

Eucalyptol is also an essential oil, it is used in mouthwashes in combination with other essential oils (Stoeken et al. 2007). 1–8 Cineole also known as eucalyptol is terpene oxide and extracted from eucalyptus species.1–8 Cineole is myorelaxant and traditionally used to treat respiratory disorders due to its secretolytic properties. The animal model has shown that when 1–8 Cineole is inhaled, it inhibits the release of cytokines and the levels of Interleukin-10 are restored to normal (Bastos et al. 2011). Side effects of 1–8 Cineole are not reported (Cai et al. 2020).

Bovine lactoferrin

Use of antibiotics along with bovine lactoferrin (100 mg) gargles before undergoing tonsillectomy in children reduced the number of group A Streptococci intracellularly in tonsils as compared to antibiotics used alone. This effect may be due to the penetration of bovine lactoferrin into the cells and increasing the apoptosis of cells (Ajello et al. 2002). The oral use of bovine lactoferrin has proved to be safe and without any side effects (Paesano et al. 2006).

Other techniques

Apart from gargling other techniques are also used to prevent respiratory infection. Oral care mouth wipes specially designed for cleaning the mouth has been used in elderly patients. The wipes did not contain an antimicrobial agent, only hyaluronic acid and trehalose were present for moisturization. These wipes significantly reduced the number of bacteria in the mouth which can be predisposing factors for pneumonia. Rinsing mouth with water with the help of a syringe followed by suction has been also used but it was less effective than the wipe method. Furthermore, the wipe method is easy to use while in the rinsing and suction method, the probability of aspiration is more (Ikeda et al. 2014). Wet wipes along with oral nutritional supplements were used in aged people in a nursing home for the prevention of aspiration pneumonia. This technique not only prevented the incidence of aspiration pneumonia but have an overall good impact on the health of the subjects (Higashiguchi et al. 2017).

In another study, three steps oral care protocol was employed which improved the oral health of the patients who were fed through the enteral route. The three steps were as; (i) tooth and tongue brushing with a toothbrush, and oral mucosa brushing using a sponge brush and 0.2% chlorhexidine solution (ii) moisturizing mouth with glyceryl polymethacrylate gel, and (iii) Salivary gland massage after step (i) and (ii). This oral care protocol reduced the incidence of pneumonia and fever. It also minimized the overall cost of the treatment by minimizing the use of antibiotics, frequency of laboratory tests, and radiological examinations (Maeda and Akagi 2014).

Purple coneflower, (Echinacea purpurea) is a medicinal plant that is used for the treatment and prophylaxis of upper respiratory infections. It has anti-inflammatory, immunomodulatory, antibacterial, and antifungal activities. Common sage (Salvia officinalis) is also used in infections and inflammation of the mouth. It has antibacterial, anti-inflammatory, antinociceptive, and astringent activities. A spray containing Echinacea and sage showed good results in the management of sore throat. Echinacea and sage have similar effectiveness as compared to chlorhexidine and lidocaine spray (Schapowal et al. 2009).

Conclusion

From minor ailments like the common cold to life-threatening respiratory infections such as influenza, gargling is beneficial. The Use of mouthwash for gargling is safe and mostly without serious side effects. There is no evidence of oral cancer with the daily use of mouthwashes that contains alcohol (Chow et al. 2017). Treating the upper respiratory tract or taking care of oral hygiene does not necessarily mean that lower respiratory infection will be prevented (Jácomo et al. 2011). The gargling agents discussed in this article have beneficial effects and helps in the management of respiratory infections. However, the use of every gargling agent is different from another. The health care providers must have the information to use which type of mouth wash or nasal irrigation in a particular respiratory infection. Despite all benefits, the mouthwashes for gargling should be used according to the needs of the individuals, or recommendations of physicians and pharmacists must be available for the people of a locality having respiratory infection outbreak. Some of the gargling agents’ may damage the epithelium and care must be taken during their use. The use of mouthwashes for gargling is not recommended in children under six years and should be used on the recommendation of physicians.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

It is a review article and the data availability statement is not applicable.