What are sunscreens?
Sunscreens protect the skin. They play an important role in blocking the absorption of ultraviolet (UV) radiation by the skin. UV radiation damages the skin and can lead to sunburns and skin cancer. But no sunscreen blocks UV radiation 100%. Sunscreens extend the length of time you can be outdoors before your skin begins to redden, but they don't give you total protection. Using sunscreen doesn't mean you can stay out in the sun indefinitely, since damage to the skin cells is still occurring.
What does the sun protection factor (SPF) mean?
The sun protection factor (SPF) on a sunscreen label is a measure of how well the sunscreen protects against ultraviolet B (UVB) rays. UVB rays are the main cause of sunburns, but like ultraviolet A (UVA) rays they can also contribute to skin cancer. The SPF on a label does not say anything about a sunscreen's ability to block UVA rays.
Higher SPF numbers mean greater protection from UVB rays, but no sunscreen can block all UVB rays. For example, a sunscreen with an SPF of 30 blocks about 97% of UVB rays, while a sunscreen with an SPF of 50 blocks about 98% of UVB rays.
How to select a sunscreen
A sunscreen protects from sunburn and minimizes suntan by reflecting UV rays. Selecting a good sunscreen is important in protecting the skin. The American Academy of Dermatology (AAD) recommends choosing a sunscreen that offers:
Broad-spectrum protection. This protects against both UVA and UVB rays.
An SPF of 30 or higher
Water resistance. This means the sunscreen provides protection while swimming or sweating for a time—either 40 or 80 minutes, depending on the label.
According to the AAD, the best type of sunscreen is any one you will use again and again. Provided that it meets the criteria above, the type you use is a matter of personal choice. Available options include lotions, creams, gels, ointments, wax sticks, and sprays.
How to apply sunscreen
Even when they use sunscreen, most people do not apply enough of it or apply it properly, which limits how useful it is. The AAD recommends the following guidelines:
Apply sunscreen to all areas of skin that will not be covered by clothing.
Use at least an ounce of sunscreen (enough to fill a shot glass) to cover exposed areas. You might need to adjust the amount depending on your body size.
Apply the sunscreen to dry skin about 15 minutes before going outdoors to give it time to be absorbed.
Reapply sunscreen at least every 2 hours, or more often after swimming or sweating.
Protect your lips by applying a lip balm or lipstick that contains sunscreen with an SPF of 30 or higher.
Remember that children need protection from the sun, too. Sunscreens are recommended for everyone over 6 months of age. For babies younger than 6 months, the American Academy of Pediatrics approves of the use of sunscreen only if adequate clothing and shade are not available. Parents should still try to avoid sun exposure and dress the infant in lightweight clothing that covers most surface areas of skin. However, parents also may apply a minimal amount of sunscreen to exposed areas, such as the infant's face and back of the hands.
Don't rely on sunscreen alone
Using sunscreen when you are going out in the sun is important, but it is only one part of an overall strategy of protecting your skin from harmful UV rays. Other important strategies to protect your skin include:
Seeking shade when appropriate. Limit your sun exposure between 10 a.m. and 4 p.m., when UV rays are the strongest.
Wearing a hat with a wide brim and tightly woven clothing that covers most of your skin, as well as sunglasses.
Avoiding tanning beds and sunlamps.