Development of essential oils as skin permeation enhancers: penetration enhancement effect and mechanism of action

Figures & data

Figure 1. Solubility of ibuprofen with the presence of different EOs (n = 3). Note: vehicle = propylene glycol (PG): isopropyl alcohol (IPA) (3:7, v/v).

Table 1. Effect of 3% w/v EO on SC/vehicle partition coefficients of ibuprofen (n = 3).

EO	Partition coefficient	Ratio^a
Vehicle	0.41 ± 0.06	1.00
Azone	0.51 ± 0.06	1.24
Turpentine oil	0.72 ± 0.01***	1.76
Angelica oil	0.51 ± 0.09	1.24
Chuanxiong oil	0.75 ± 0.01***	1.83
Cyperus oil	0.68 ± 0.09*	1.66
Cinnamon oil	0.80 ± 0.12**	1.95
Clove oil	0.98 ± 0.07***	2.39

* p < 0.05,

** p < 0.01,

*** p < 0.001 vs. the vehicle group.

^a Ratio = (partition coefficient with 3% w/v EO treatment)/(partition coefficient with vehicle treatment).

Figure 2. Permeation profiles of ibuprofen with 3% w/v EOs through excised rat skin (n = 5).

Table 2. The percutaneous permeation parameters of ibuprofen with various EOs through excised rat skin (n = 5).

PE	Flux/μg·cm^−2·h^−1	ER	Tlag/h	Permeation ratio^a/%
Vehicle	9.94 ± 3.36	1.00	7.49 ± 0.37	47.09 ± 11.90
Azone	19.49 ± 2.66**	1.77	7.28 ± 0.93	56.22 ± 12.56
Turpentine oil	24.54 ± 7.90**	2.23	6.16 ± 0.70**	68.80 ± 17.16*
Angelica oil	20.22 ± 5.29**	1.83	7.57 ± 0.27	79.43 ± 5.36***
Chuanxiong oil	28.61 ± 7.66**^#	2.60	7.94 ± 0.29	88.41 ± 4.12***^#
Cyperus oil	27.37 ± 7.07**^#	2.49	7.03 ± 0.73	70.72 ± 15.57*
Cinnamon oil	28.93 ± 7.21***^#	2.63	7.78 ± 0.56	81.08 ± 2.09***
Clove oil	21.64 ± 8.00*	1.97	7.52 ± 0.53	71.24 ± 15.85*

^a Cumulative amount of permeated ibuprofen at 48 h/added ibuprofen*100%.

* p < 0.05,

** p < 0.01,

*** p < 0.001 vs. the vehicle group,

# p < 0.05 vs. the Azone group.

Figure 3. ATR-FTIR absorption spectra of rat skin treated with 3% w/v EOs.

Table 3. Peak positions of SC lipids after treated with 3%EOs (n = 3).

	Peak position of lipid (cm^−1)		The shift of peak position (Δcm^−1)^a
PE	Asymmetric C-H stretching	Symmetric C-H stretching	Asymmetric C-H stretching	Symmetric C-H stretching	Total of the decrease
Blank	2917.05 ± 1.15	2849.58 ± 0.31	0	0	0
Vehicle	2919.83 ± 0.76	2850.14 ± 2.28	2.83	0.56	3.39
Azone	2925.17 ± 2.03	2851.23 ± 0.52	8.12	1.65	9.77
Turpentine oil	2923.23 ± 1.28	2850.33 ± 1.24	6.18	0.75	6.93
Angelica oil	2921.72 ± 2.72	2849.80 ± 1.99	4.67	0.22	4.89
Chuanxiong oil	2923.94 ± 2.76	2851.28 ± 0.20	6.89	1.70	8.59
Cyperus oil	2921.98 ± 1.02	2851.04 ± 0.24	4.93	1.46	6.39
Cinnamon oil	2922.86 ± 2.76	2851.58 ± 1.48	5.81	2.00	7.81
Clove oil	2920.75 ± 0.24	2850.87 ± 1.51	3.70	1.29	4.99

^a Shift in peak position compared to the untreated skin treated (Blank).

Table 4. Peak areas of SC lipids after treated with different EOs (n = 3).

	Peak area		The decrease of peak area^a
PE	Asymmetric C-H stretching	Symmetric C-H stretching	Asymmetric C-H stretching	Symmetric C-H stretching	Total of the decrease
Blank	84.12 ± 1.94	33.47 ± 3.14	0	0	0
Vehicle	81.77 ± 0.97	36.99 ± 0.62	−2.35	3.52	1.17
Azone	61.39 ± 5.14	25.38 ± 9.64	−22.73	−8.09	−30.82
Turpentine oil	33.72 ± 4.65	15.77 ± 7.00	−50.40	−17.70	−68.10
Angelica oil	40.61 ± 0.56	15.11 ± 2.00	−43.51	−18.36	−80.23
Chuanxiong oil	38.58 ± 7.98	12.96 ± 4.12	−45.54	−20.51	−66.05
Cyperus oil	44.41 ± 0.77	14.74 ± 3.34	−39.71	−18.73	−58.44
Cinnamon oil	28.60 ± 3.81	8.89 ± 0.97	−55.52	−24.58	−80.1
Clove oil	33.09 ± 12.33	10.33 ± 0.44	−51.03	−23.14	−74.07

^a Decrease in peak area = peak area of EO treatment–peak area of blank.

Figure 4. The relationship between ER values and the total of the shift of peak position (A) or the total decrease of peak area (B) after EOs treatment.

Figure 5. Effect of EOs with different concentrations on HaCaT keratinocyte cell viability in vitro (n = 6).