Caffeine counteracts UV-induced damage to the hair follicle

This study was the first to show that UV radiation also causes significant damage to hair follicles. Specifically, it was demonstrated that UV rays reduce the proliferation of cells in hair follicles, leading to cell damage and the premature transition to the inactive hair growth phase.

Caffeine, on the other hand, was able to reduce these negative effects by decreasing cytotoxic cell damage and cell death, as well as inhibiting the transition to the inactive hair growth phase.

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, much less is known about the influence of UV radiation on the functionality of hair follicles in the skin.

The aim of this investigation was to establish a model system in which hair follicles with their surrounding skin tissue (full thickness scalp skin) were cultured as a functional organ (ex vivo) and to determine the damage to the hair follicles caused by the application of ultraviolet radiation (UV). The intensity of the applied UVA radiation (320-400 nm) and UVB radiation (280-320 nm) was comparable to sun exposure levels in July in Europe.

The further course of this investigation aimed to demonstrate the positive influence of caffeine on UV-damaged hair follicles.

For the investigation, 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 then cultured again for 3 days with or without caffeine (0.1 %). The low UV dosage corresponded to sun exposure of approximately 30 minutes in July in Europe (France or Germany), while the high dosage corresponded to sun exposure of more than 60 minutes.

Similar to previous studies, UV radiation had a significant impact on the damage to the outermost skin layer (epidermis) as well as the general skin damage. Treatment with low and high UV dosages also led to oxidative DNA and cell damage (cytotoxicity) in the hair follicles. Furthermore, the proliferation of keratin-forming cells (keratinocytes) in the hair matrix (HM) and the outer root sheath (ORSK) was reduced, cell death was more frequently triggered, and the transition to the inactive hair growth phase (catagen) was initiated. The higher UV dosage resulted in significantly more severe damage and reached much deeper areas of the hair follicles.

Interestingly, the topical application of caffeine led to a reduction in UV-induced cytotoxic cell damage and a decrease in the cell death rate of keratin-forming cells (keratinocytes) from the hair matrix (HM) and the outer root sheath (ORSK). At the same time, the transition to the inactive hair growth phase (catagen) was inhibited.

The results of this investigation highlight the negative effects of UV radiation on the skin and, for the first time, the proven UV-induced damage to hair follicles. Therefore, preventive measures should be taken not only to protect the skin but also specifically to protect the hair follicles to avoid UV damage to the body and scalp. In the course of this investigation, it was also shown for the first time that caffeine can counteract UV-induced damage in hair follicles and could be beneficial as an addition to sun protection products.