Part of the sun's energy that reaches earth is composed of rays of invisible ultraviolet (UV) light. When ultraviolet light rays (UVA and UVB) enter the skin, they inflict both visible and invisible damage to the skin cells.
Of the invisible damage to skin cells, some is repaired but some adds up year after year. After 20 to 30 years or more, the built-up damage appears as wrinkles and age spots. Although window glass blocks UVB light, UVA rays are able to pass through it.
Because risk increases according to total lifetime sun exposure, older people are much more likely to develop actinic keratoses.
Of all factors that contribute to wrinkle formation, none surpasses the destructive force of excessive sun exposure. Shunning the two distinct yet equally harmful UV rays – A and B – is the first step to maintaining youthful skin. UVB rays are responsible for visible sunburn, yet UVA rays are just as damaging, even though they cause little skin redness. This type of radiation penetrates the skin, causing cellular damage that accumulates slowly over a period of time. UVA rays induce the formation of free radicals, which attack the skin's lipids. The resulting damage gives rise to visible signs of aging such as wrinkles and leathery skin.
Drinking four or more cups of green tea each day may help stave off skin cancer. This substance could be similarly effective if incorporated into skin care creams, but the quantity and consistency of EGCG (active compound found in green tea) should be questioned.