Damage to hair follicles by UV rays and the protective effect of caffeine
While the effects of ultraviolet (UV) radiation on human skin have been extensively studied and preventive measures to protect the skin under sun exposure are ubiquitous, far less is known about the influence of UV radiation on the functioning of hair follicles in the skin.
The aim of this study was to establish a model system in which hair follicles with their surrounding skin tissue (full thickness scalp skin) were cultivated as a functional organ (ex vivo) and the damage to the hair follicles was determined by the application of ultraviolet radiation (UV). The intensity of UVA radiation (320-400 nm) and UVB radiation (280-320 nm) applied was comparable to sunlight exposures in July in Europe.
In the further course of this examination, the positive influence of caffeine on UV-damaged hair follicles should be proven.
Methods
For the study, human skin biopsies with terminal hair follicles were cultured for 3 days with or without caffeine (0.1%). Subsequently, the biopsies were treated with different intensities of UVA and UVB radiation and cultured again for 3 days with or without caffeine (0.1%). The low UV dosage corresponded to a comparable sunlight exposure of about 30 minutes in July in Europe (France and Germany, respectively), with the high dosage corresponding to sunlight exposure of more than 60 minutes.
Results
Comparable to previous studies, UV radiation had a major influence on the damage to the uppermost layer of the skin (epidermis) as well as the general damage to the skin. The treatment with low and high UV dosage also led to oxidative DNA and cell damage (cytotoxicity) in the hair follicles. Furthermore, the proliferation of the horn-forming cells (keratinocytes) of the hair matrix (HM) and the outer hair root sheath (ORSK) was reduced, cell death was triggered more frequently and the transition to the inactive hair growth phase (katagenic) was initiated. In each case, the higher UV dosage resulted in significantly greater damage and reached much deeper areas of the hair follicles.
Interestingly, topical application of caffeine led to a reduction in UV-induced cytotoxic cell damage as well as to a reduction in the cell death rate of horn-forming cells (keratinocytes) from the hair matrix (HM) and from the outer hair root sheath (ORSK). At the same time, the transition to the inactive hair growth phase (katagenic) was inhibited.
Summary
The results of this study illustrate the negative effects of UV radiation on the skin and, for the first time, the proven UV-induced damage to the hair follicles. Accordingly, preventive measures should be taken not only to protect the skin, but also the hair follicles in particular to avoid UV damage to the body and head. As part of this study, it was also shown for the first time that caffeine can counteract UV-induced damage in the hair follicle and could be helpful as a supplement to sun protection products.
PUBLISHED STUDY
- J. Gherardini, J. Wegner, J. Chéret, S. Ghatak, J. Lehmann, M. Alam, F. Jimenez, W. Funk, M. Böhm, N. Botchkareva, C. Ward, R. Paus, M. Bertolini, In J Cosm Sci, 2019.