The observed changes within solar lentigines

Solar lentigines, also known as sun spots or age spots, are due to prolonged and repeated exposure to the sun's UV rays. Indeed, when our skin is exposed to the sun, melanocytes produce melanin, a pigment responsible for the colour of our tan. When melanin is produced in excess, it will eventually accumulate and form these brown spots called solar lentigines. They are mostly found on the backs of the hands, the décolletage, the face, the shoulders and the back.

Furthermore, lentigo can also be caused by skin ageing. With age, the skin fails to fully protect itself from external aggressions and deteriorates. Free radicals attack the nuclei of melanocytes and mitochondria. We observe a malfunction of the melanocytes associated with the exhaustion of their pigmentary potential at the level of the hair bulbs. The skin thus becomes more vulnerable to UV rays, promoting the formation of sun spots or age spots. Be aware, the use of certain photosensitising medications can promote lentigos.

The term keratosis refers to a skin condition also known as keratoderma or hyperkeratosis when the keratosis is very thick. It corresponds to an excessive development (hypertrophy) of the superficial layer of the epidermis, the horny layer, the main component of which is keratin. This latter is formed at the level of the keratinocytes.

Seborrheic keratoses are often pigmented superficial epithelial lesions. This skin growth is primarily located on friction areas, notably the chest and face. They initially appear, as beige or brown spots, or solar lentigines, then darken and gradually thicken. Although their origin involves genetics, the sun plays a predominant role in promoting their proliferation. Despite their wart-like appearance, these lesions are benign and harmless.

The lichenoid keratosis or lichen planus-like keratosis is a skin lesion in the form of a solitary, oval or round bump. It resembles a warty or painful growth, red or inflamed, or, on the contrary, a scaly and dry spot. Although its cause remains unknown, an inflammatory reaction is generally considered. It occurs when the immune system is directed against the skin following excessive exposure to UV rays, among other things.

Lichenoid keratosis can also be promoted by the presence of pigmented sunspots or solar lentigines, and by a benign skin growth, seborrheic keratoses. Indeed, a clinical study has asserted that solar lentigines are the most common precursors of a lichenoid keratosis with a solar lentigo present in 29 of the 59 patients affected by a lichenoid keratosis.

GOLDENHERSH M. A. & al. Documented evolution of a solar lentigo into a solitary lichen planus-like keratosis. Journal of Cutaneous Pathology (1986).

ELGART G. W. SEBORRHEIC KERATOSES, SOLAR LENTIGINES, AND LICHENOID KERATOSES. Dermatologic Clinics (2001).