How does sunscreen works?

Answer 1

Sunscreens work by absorbing, reflecting or scattering ultraviolet light, thereby reducing the amount that reaches the skin. The sun protection factor (SPF) of a sunscreen tells you how much longer you can stay in the sun without burning if you apply the sunscreen. For example, if your child would burn after 20 minutes of sun exposure, applying a sunscreen with a SPF of 15 gives her 15 times the protection. In this example, the child will be protected for up to 5 hours: 20 minutes x 15 SPF = 300 minutes (5 hours).

The FDA recommends that kids use a SPF of 15 or higher to prevent both sunburn and tanning. A SPF of 15 will block about 94 percent of UVB rays and a SPF of 30 will block about 97 percent of UVB. But keep in mind that these SPF ratings do not necessarily mean your child will be protected against the UVA rays that cause cancer and skin damage. SPFs only give a rating of sunburn protection. Your sunscreen should include ingredients that protect against both UVA and UVB rays.

Answer 2

According to chemistry.about.com: "Sunscreen combines organic and inorganic chemicals to filter the light from the sun so that less of it reaches the deeper layers of your skin. Like a screen door, some light penetrates, but not as much as if the door wasn't present. Sunblock, on the other hand, reflects or scatters the light away so that it doesn't reach the skin at all."