The main source of human skin exposure to ultraviolet radiation (UVR) is the sun, but people are also exposed to UVR in phototherapy and through the use of tanning devices. UVR has many important acute and long‐term effects on the skin. The most evident acute effects are erythema and tanning; skin cancer and photoageing are the long‐term effects. Acute and long‐term effects are dependent on the genetically determined skin type. All photobiological effects are initiated by the absorption of UVR energy by molecules in the skin called chromophores, of which DNA is an important example. Most of the effects of UVR on the skin are considered to be detrimental, but the synthesis of vitamin D is the only well‐established beneficial effect. Adequate photoprotection, which includes shade seeking, sunscreens and clothing, can reduce the adverse effects of UVR, whilst still allowing vitamin D synthesis.

Keywords ultraviolet radiation, UVR, emission spectrum, dosimetry, chromophores, action spectrum, skin type, sunburn, erythema, tanning, sunbed, DNA photodamage, skin cancer, photoageing, vitamin D, blood pressure, sunscreens, photoprotection