Melatonin immunoreactivity of epidermal skin is higher in the evening than morning but does not account for erythema sensitivity

ABSTRACT

The skin is a site of melatonin synthesis, and melatonin has a role in protecting against ultraviolet radiation-induced damage. Ultraviolet B (UVB) induced erythema seems to vary between morning and evening. We investigated whether epidermal melatonin immunoreactivities in the morning differed from those in the evening, and whether UVB-induced erythema was associated with these melatonin immunoreactivities in healthy volunteers. Erythema sensitivity of the skin was determined in the morning and in the evening by scoring the Minimal Erythema Dose and quantifying the erythema index (EI). We took biopsies from the non-UVB-exposed skin of healthy volunteers (n = 39) in the morning and in the evening to study melatonin immunoreactivity with immunohistochemistry (IHC). In the IHC staining, there was more melatonin immunoreactivity in the evening than in the morning (p < .001). Erythema was more pronounced in the evening than in the morning irradiated skin (p < .001). The graded amount of melatonin immunoreactivity in the samples was not associated with the EI. We discovered melatonin immunoreactivity of the non-irradiated skin to vary diurnally. However, endogenous skin melatonin does not seem to be the reason why NB-UVB induces more erythema in the evening than in the morning.

KEYWORDS:

• Ultraviolet radiation
• skin
• melatonin
• circadian clock
• circadian rhythms
• immunohistochemistry
• erythema

Acknowledgements

We gratefully acknowledge our research nurse Ulla Oesch-Lääveri and laboratory analyst Eini Eskola for their dedication and help in the implementation of the study.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/07420528.2022.2157733

Additional information

Funding

This study was financially supported by the Competitive State Research Financing of the Expert Responsibility Area of Tampere University Hospital.