Can the sun improve the signs of keratosis pilaris?

Keratosis pilaris is a skin condition that manifests as small red or white bumps. The skin then becomes rough to the touch and has an appearance similar to that of sandpaper. Non-contagious, keratosis pilaris can develop on different parts of the body. However, it is most commonly found on the arms, legs and buttocks. It is important to note that keratosis pilaris poses no health risk and the main concern is aesthetic. In rare cases, those affected complain of mild itching.

Keratosis pilaris results from an overproduction of keratin by the keratinocytes of the epidermis which will clog the hair follicles. Although the causes of this skin issue are still under study, a component genetic is strongly suspected. It has indeed been observed that keratosis pilaris develops more frequently in individuals with a family history of this condition. Several solutions exist to alleviate the symptoms of keratosis pilaris: is sun exposure one of them?

It is true that individuals affected by keratosis pilaris generally notice an improvement in their symptoms during the summer. Several factors can explain this phenomenon, among which is the tanning induced by the sun. Indeed, upon penetrating the epidermis, UV rays trigger several biological reactions including the binding of the melanotropic hormone (MSH) to the melanocortin 1 receptor (MCR1), located on the membranes of melanocytes. This binding triggers a cascade of reactions, resulting in the synthesis of melanin, the brown pigment responsible for skin colouration. To a certain extent, this can camouflage imperfections and help to make the rough bumps of keratosis pilaris less visible.

Furthermore, in defence against UV rays, the epidermis also tends to thicken. This thickening of the stratum corneum is a result of a rapid differentiation of keratinocytes under the influence of UV, leading to an intensification of the keratinisation of the epidermis. This is an adaptive response, a thicker skin having a better capacity to dissipate ultraviolet rays, which reduces damage to deeper cellular components. This thickening has the effect of masking small bumps associated with keratosis pilaris.

Even though the sun may temporarily help to reduce the signs of keratosis pilaris, it is important to remember that UV rays have a detrimental effect on the skin in the long term.

In a manner akin to acne, the effects of the sun on keratosis pilaris only last for a season. As summer draws to a close and the sun shines less brightly in the sky, the epidermis thins out to regain its initial thickness. The follicular plugs associated with keratosis pilaris then become clearly visible again and the skin resumes its rough texture.

Furthermore, UV rays are responsible for significant cellular damage and cause redness, even sunburns of varying degrees of pain. If we add to this an increased risk of skin cancer, deeper wrinkles and other harmful effects, it becomes clear that it is better to avoid excessive sun exposure and to always apply sun protection in sufficient quantity. There are other solutions, safer ones, to alleviate the symptoms of keratosis pilaris.

• KHOPKAR U. S. & THOMAS M. Revisiting Keratosis Pilaris: Is It More Than Just a Follicular Keratosis? International Journal of Trichology (2012).

• WANG J. F. & ORLOW S. J. Keratosis Pilaris and its Subtypes: Associations, New Molecular and Pharmacologic Causes, and Treatment Options. American Journal of Clinical Dermatology (2018).

• FELDMAN S. R. & al. Treatment of keratosis pilaris and its variants: a systematic review. Journal of Dermatological Treatment (2022).