The summer sun produces different kinds of rays -- two of which can cause severe skin damage and even skin cancer.
According to University Health Services at the University of California, the most dangerous kind of exposure comes from UVB rays, which have shorter wavelengths and are primarily responsible for sunburn. Repeated exposure to UVB over a lifetime can alter the immune system and can lead to melanoma and basal and squamous cell carcinoma, three forms of skin cancer.
UVB primarily affects the skin's outer layers and tend to be more intense during the summer month, at higher altitudes, and as you get closer to the equator. Less harmful are UVA rays, which are longer-wavelength rays that can damage the skin's connective tissue, leading to premature aging as well as playing a role in causing skin cancer.
UVA rays, the type used in tanning salons, also increase the risk of cataracts and retinal damage. Although experts still believe UVB is responsible for much of the skin damage caused by sunlight -- especially sunburn -- UVA may be an important factor in other types of sun damage, including photo aging and the development of skin cancers.
Most sunscreens do a good job blocking UVB but are less effective against UVA wavelengths, which may also contribute to skin cancer.
With approximately 65 percent of melanomas and 90 percent of basal and squamous cell skin cancers attributed to UV exposure, scientists must still figure out how best to formulate sunscreens to provide effective protection against both UV wavelengths.