Sunscreens are products that protect the skin from ultraviolet radiation (UVR.)
They do this by using 1) organic chemicals that absorb light and dissipate it as heat such as Avobenzone, 2) inorganic filters or blockers which sit on the surface of the skin and act as a physical barrier to UVR such as Zinc Oxide or Titanium Dioxide or 3) a combination of both.
There are three types of ultraviolet radiation:
UVB: These rays are primarily responsible for sunburn and suntan. Long-term exposure to UVB rays leads to premature aging of the skin and skin cancer.
UVA: These rays are primarily responsible for premature aging and skin cancers such as melanoma and basal cell carcinoma.
UVC: These rays are absorbed by the earth’s atmosphere.
Sunscreens are important in the following ways:
Sunscreens which contain a Sun Protection Factor (SPF) of 30+ filter 97% of UVB rays. However, the SPF rating does not tell you anything about the sunscreen’s ability to protect you from harmful UVA rays. Both UVA and UVB rays are more effectively blocked by sunscreens that contain at least 6% Zinc Oxide, Titanium Dioxide or Avobenzone. A sunscreen may state that it is a “broad-spectrum” product only if it meets FDA standards for both UVB and UVA protection. Only broad-spectrum sunscreens with an SPF of 15 or higher may state that they protect against skin cancer if used as directed with other sun protection measures.
Sunscreens should all be applied to DRY skin prior to going outside. All sunscreens begin to come off during activity so it is very important to reapply the sunscreen approximately every two hours. No sunscreen provides all-day protection. A sunscreen company cannot claim that it provides sun protection for more than 2 hours without submitting test results to prove this.
"Water-resistant” sunscreens have completed only either a 40 or 80 minute still-water bath test and must specify which time test was passed. There are no truly waterproof or sweat proof sunscreens. Sunscreens that are not water-resistant must instruct consumers to use a water-resistant sunscreen if they are swimming or sweating. The terms “sweat proof” and “waterproof” are no longer allowed on sunscreen labels.
Sunscreens with an SPF higher than 30+ don’t necessarily offer better protection from the sun. Remember that the SPF reflects only your degree of protection from UVB rays. Both UVA and UVB rays are blocked by Zinc Oxide, Titanium Dioxide or Avobenzone. Higher SPF sunscreens may provide no more protection from UVA rays and may contain large amounts of organic components which can increase the potential for irritation, especially in children.
The term “sunblock” is a misnomer and is no longer allowed on sunscreen labels. No sunscreen blocks ALL sun from the skin. Unless your sunscreen is applied as a thick paste, it will still allow a little UV light to penetrate the skin.