THE SOLAR electromagnetic spectrum ranges widely from below the short ultraviolet wavelength through the visible light spectrum and beyond. The ozone in our stratosphere 25 km above the earth effectively protects us from the short-wave, highenergy ultraviolet (UV) light. But UV light that does penetrate the atmosphere contains the erythrogenic spectrum that causes the all-too-familiar sunburn reaction.
Redness begins two to eight hours after exposure and usually peaks at 24 hours. When the exposure has been longer than five times the minimum erythema dose (MED) (ie, the amount of energy from a defined light source, like the sun, producing a barely perceptible sunburn or erythema of the skin under stated conditions), blistering, pain, and fever may also occur. Although immediate darkening of pigment may accompany such erythema, due to oxidation of colorless preformed melanin already in the skin, it is transient, fading within a few hours. The socially sought-after, durable
Kaminester LH. Sunlight, Skin Cancer, and Sunscreens. JAMA. 1975;232(13):1373-1374. doi:10.1001/jama.1975.03250130055026