Why does skin become red and sensitive from excessive sun exposure? And why are red-haired people even more affected by these sunburns? Two in-depth studies lift the veil on the mechanisms involved in the inflammation caused by ultraviolet rays. A paradoxical phenomenon, sunburn is an inflammatory reaction which, by eliminating dead cells and those with genetic alterations, triggers a process of healing of skin cells.
It has long been known that the harmful effect of excessive sun exposure is due to UVB rays: by interacting directly with skin cells, these high-energy rays cause inflammation characterized by redness (erythema) and, in some cases, to genetic alterations that increase the risk of melanoma. However, the sequence of events involved in this response of skin cells to UV radiation remains largely unknown.
To solve this enigma, American researchers subjected skin cells to UVB rays and examined the formation of molecules capable of activating the production of TNF, a
inflammatory agent suspected of playing an important role in the sunburn phenomenon associated with prolonged exposure to the sun. They made the astonishing discovery that UVB rays break down small non-coding RNA molecules (which are not translated into proteins) located in the cell nucleus. The irradiated cells release the broken RNA, which prompts nearby healthy cells to manufacture TNF to trigger the inflammatory response to eliminate sun-damaged cells. This inflammatory reaction triggers the healing process by eliminating dead cells as well as those with genetic alterations, before they become cancerous.
In other words, sunburn is the visible (and painful) manifestation of a healing reaction triggered by healthy cells in response to the breakdown of RNA molecules caused by UVB rays. However, this mechanism is not perfect and it goes without saying that repeated sunburns increase the risk that damaged cells escape this cleaning process and become cancerous. It is therefore essential to always use protective sun creams or even put on clothing before exposing yourself to the sun, especially in the middle of the day when the radiation is at its maximum.
Fair skin, red, even more precautions to take
These recommendations are especially important for people who have very pale skin, red hair and freckles. These characteristics are caused by a genetic variation that controls the production of pigments in the skin. Instead of generating the eumelanin, a brown/black pigment that blocks UV rays, skin cells called melanocytes produce pheomelamine, without protective properties, so it is very important for these people to avoid prolonged exposure to the sun without protection.
Recent research shows that red-haired people have an increased risk of melanoma, even in the absence of UV radiation. Researchers have noted that a genetic variation leading to the synthesis of red pigment causes increased DNA damage to skin cells as well as an increased incidence of invasive melanoma, even in the absence of UVB. Pheomelanin is therefore capable of inducing the formation of melanomas by itself, possibly by stimulating a mechanism that causes oxidative stress in skin cells.
At the skin cell level. In addition to avoiding unprotected exposure to the sun, red-haired people therefore benefit from adopting certain lifestyle habits that minimize this oxidative stress, for example by abstaining from smoking and eating healthy foods. In this sense, it is interesting to note that green tea, foods rich in carotenoids such as tomatoes, whose lycopene is distributed in the skin, and certain fruits such as pomegranate or grapes all have antioxidant and anti-inflammatory actions. which could help reduce the risk of melanoma in these people.
Bernard JJ et al. Ultraviolet radiation damages self noncoding RNA and is detected by TLR3. NatureMedicine; 18: 1286–1290.
Mitra D et al. An ultraviolet-radiation independent pathway to melanoma carcinogenesis in the red hair/fair skin background. Nature 491: 449-543