Vitiligo: is sun exposure dangerous?

Can exposure to sunlight favour the progression of vitiligo?

The vitiligo is an autoimmune disease characterised by the destruction of melanocytes, the cells responsible for producing melanin, thus leading to the depigmentation of certain areas of the body. Although genetic predispositions are largely involved in its development, several environmental factors may also promote the onset of vitiligo. Among these, sun exposure is cited as a potential trigger, due to the oxidative stress it can induce in melanocytes.

However, phototherapy is one of the most widely used approaches to promote repigmentation of vitiligo lesions.

PUVA phototherapy, combining psoralen and UVA rays, works by modulating the immune response, notably reducing the activity of T lymphocytes. In turn, narrowband UVB phototherapy (NB-UVB) stimulates the proliferation and migration of melanocytes still present in adjacent areas. However, uncontrolled sun exposure can cause sunburn or local inflammation, which may aggravate existing lesions, particularly through the Koebner phenomenon, where skin trauma triggers the appearance of new patches.

A study conducted on 442 vitiligo patients, distributed across different phototypes (I to VI), analysed their perception of solar risk. Among them, 86 patients stated that their patches appeared more visible after exposure, and 113 believed their depigmented areas were more vulnerable to sunburn. These observations reflect a common subjective experience among patients. Furthermore, they often consider that vitiligo increases the risk of developing melanoma.

Contrary to what one might expect, vitiligo appears to reduce cancer incidence, since the autoimmunity induced by vitiligo seems to confer protection against melanomas. Moreover, patients with vitiligo often have better reflexes for photoprotection.

Indeed, a large-scale 2014 study analysed a cohort of 10 040 patients with vitiligo to assess their risk of skin cancer compared with a control group. The findings revealed a markedly lower incidence of skin cancer in individuals with vitiligo. However, the study also identified an increased risk of cutaneous cancers in patients who had undergone phototherapy sessions (14.1% versus 3.2%).

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3.8% and 1.1%

This concerned the respective risks of non-melanoma skin cancers and melanomas in individuals with vitiligo.

19.6% and 4.5%

It represented the risk of non-melanoma skin cancers and melanomas in individuals without vitiligo.

Does exposure to sunlight increase the risk of vitiligo?

Another widespread misconception is that sun exposure favours the onset of vitiligo in individuals without any existing lesions.

A study published in the Journal of Investigative Dermatology and conducted with 51,337 participants revealed that individuals with a high capacity to tan, that is to say a phototype dark, may have an increased risk of developing vitiligo, owing to a genetic variation in the TYR gene, which encodes tyrosinase, a key enzyme in melanogenesis. In addition, reduced levels of glutathione peroxidase (GPx), an essential enzyme for neutralising reactive oxygen species responsible for oxidative stress – a factor implicated in the development of vitiligo – were observed in these women. This correlation may explain their heightened susceptibility to the disease.

Research also suggests that individuals who endured severe sunburn after more than two hours of sunlight exposure during childhood have an increased risk of developing vitiligo. A study published in the British Journal of Dermatology revealed that, among 177 patients surveyed, 51 identified the sunburns as a trigger for the disease, that is to say, the initial depigmented lesions appeared shortly after the severe sunburn. However, the small sample size and the subjective nature of these reports do not permit firm conclusions.

When the skin is exposed to UV radiation, it undergoes cellular stress that leads to the production of heat shock proteins, notably HSP70i. Overexpression of this protein has been associated with a depigmenting autoimmune response, potentially prompting the immune system to attack melanocytes. Severe sunburns from prolonged sun exposure may thus trigger a chain reaction involving HSP70i, fostering both an autoimmune response and oxidative stress that increase cellular damage. Moreover, the Koebner phenomenon, in which skin trauma encourages the appearance of new vitiligo lesions, may also play a role in the disease’s development.

However, further studies are required to confirm these mechanisms and to gain a better understanding of the link between sun exposure and the onset of vitiligo.