Effects of Sunlight on Human Skin
At the skin level, sunlight—particularly its ultraviolet (UV) component—may produce both beneficial and harmful effects.
Beneficial Effects
Vitamin D synthesis
UVB radiation stimulates the production of a vitamin D precursor in the skin.
Through subsequent metabolic processes in the liver and kidneys, this precursor is converted into vitamin D.
Mood improvement
Sunlight promotes endorphin production and helps reduce stress.
Phototherapy
Sunlight may improve skin diseases such as psoriasis, atopic dermatitis, and vitiligo.
Harmful Effects
Sunburn
Simple erythema (redness), swelling, blistering, and burns.
Photodermatoses
Sunlight-related disorders, including genetic or metabolic diseases
(e.g. xeroderma pigmentosum and porphyrias), immunological diseases
(e.g. solar urticaria and polymorphic light eruption), reactions mediated
by chemicals or drugs (e.g. phototoxic and photoallergic reactions), and
skin or systemic diseases aggravated by light (e.g. lupus erythematosus,
dermatomyositis, and herpes simplex).
Photoaging
Dark or light spots, wrinkles, dryness, thinning or thickening of the skin,
and dilated capillaries in sun-exposed areas.
Immunomodulation
Immunosuppression.
Photocarcinogenesis
Development of basal cell carcinoma, squamous cell carcinoma, melanoma,
and actinic keratoses.