When used generously and appropriately, sunscreen products and sun avoidance help reduce the severity of many aging skin disorders, including squamous cell cancers. There are certain concerns, however.
Sunscreen Use May Not Protect against Basal Cell and Melanoma Cancers–and May Even Increase the Risk. Although sunscreens help prevent squamous cell carcinomas and other skin disorders, sunscreens do not appear to provide protection against melanoma and some basal cell cancers. In fact, some studies have reported a higher association with sunscreen use and these skin malignancies, though not all studies report such negative results. The reasons for this possible increased risk are unclear, though some theories include the following:
Until recently, many sunscreens blocked only or predominantly UVB rays and not UVA, the more deeply penetrating rays now known to be especially dangerous. (Most major sunscreen brands now block both UVA and UVB, but the effect of this double action on melanoma is not yet clear.)
People who apply sunscreens may feel safe and stay out longer during high sun-exposure hours than is safe. It should be strongly noted that even if a person doesn’t sunburn, UVA rays can still penetrate the skin and do harm.
People do not put on enough sunscreen. In fact, according to one survey most apply about one quarter of the amount needed to meet standard recommendations for sun protection.
Some sunscreen products, notably those containing PABA, may actually break down in the presence of UV exposure and release harmful free radical particles, which theoretically could increase the risk for cancer, though the long-term effects are not known. (Still other evidence suggests that some sunscreen ingredients protect against such oxidants.)
Sunscreens Use May Increase the Risk for Health Problems Related to Sunlight Deficiencies. There is some major concern that underexposure to sunlight, due to the use of sunscreens or sun-avoidance measures, may produce other health problems, such as the following:
Vitamin D Deficiency. Vitamin D is found in foods, but it is primarily manufactured a chemical reaction to ultraviolet B sunlight. Vigorous sun-protection measures, then, may increase a person’s risk for developing vitamin D deficiency. Vitamin D is important for prevention of rickets and osteoporosis and some cancers, including melanoma . People who need to avoid sunlight and whose diet is low in foods that contain vitamin D should take supplements. People with darker skin are at higher risk for deficiencies from sun protection than those with whiter skin. (Note: vitamin D is toxic in high doses.)
Other Cancers. Although sunlight is implicated in skin cancers, it is also associated with lower risks for breast, prostate, ovarian, and colon cancers. Some protection against these cancers may be related to vitamin D production by sunlight.
Depression. Many people suffer from SAD (seasonal affective disorder), a form of depression that generally occurs in winter and is associated with exposure to less sunlight.
The bottom line is that some sunlight is important and even necessary for a healthful and high-quality life. Some experts recommend that adults may benefit from daily moderate tanning (20 to 30 maximum minutes of exposure during lower-risk hours) over a number of days to slowly build up pigment in the skin.