What does spf

It's ideal for doing things like walking your dog or running errands. But if you plan to do any outdoor activities like hiking or swimming, be sure to go for SPF And make sure you always stick to a broad-spectrum sunscreen. If you don't see broad-spectrum on the label, then the sunscreen may not protect you from UVA rays. In fact, in order to get proper coverage from spray sunscreens, you'd need to spray each area — legs, feet, back, arms, shoulders, etc. Instead of sprays, choose thick lotions and slather them on 15 minutes before you go outside to let them soak into your skin.

Regardless of what SPF you're using, you should reapply sunscreen every two hours if you're spending a lot of time outside. Also, make sure the sunscreen is water-resistant if you know you're going to be sweating. If you just went swimming, apply immediately after since water-resistant does not mean waterproof. The amount of light that induces redness in sunscreen-protected skin, divided by the amount of light that induces redness in unprotected skin is the SPF.

A higher SPF doesn't indicate superior sun protection—it indicates that you will remain protected in the sun for a longer amount of time. However, SPF 2 sunscreen will need to be applied more frequently.

To be safe, no matter what SPF you choose, it's best to reapply sunscreen at least every two hours, as well as after swimming or sweating. However, ultraviolet A UVA rays also pose risks. They age the skin and contribute to skin cancer. Wearing sunscreen with an adequate SPF, and doing so properly, is key to protecting your skin. But the clothing you wear is also important. Generally speaking, long sleeves and pants are more protective than tank tops and shorts. But even if you're covered in clothing from head to toe, there is a chance that sun can make its way right through fabric fibers.

When some fabrics are examined under a microscope, especially if they are made from fibers knitted or woven together, space between fibers is visible. UV rays can penetrate through those spaces and reach skin. The more tightly knit a fabric is, such as denim, the less likely UV rays can get through.

The less tightly knit a fabric is, such as linen, the more likely UV rays can get through. If you opt for lightweight, summery fabrics, you should still apply sunscreens even on parts of the body that are covered up. Wearing sun-safe clothing is a great additional measure you can take beyond wearing sunscreen to help protect your skin from the sun. UPF clothing is made with fabric that protects skin from the sun.

Wang is a board-certified dermatologist with fellowship training in melanoma, Mohs surgery, dermatologic surgery and laser surgery. He is actively involved in clinical research, with a focus on photoprotection and the development of noninvasive imaging technologies to diagnose skin cancer.

How high should I go? UVA rays cause skin damage that leads to tanning as well as skin aging and wrinkles. The shortest wavelengths of UVA rays also contribute to sunburn. Updated June 9, About the expert: Steven Q. SPF is actually a measure of protection from amount of UVB exposure and it is not meant to help you determine duration of exposure. Using half the required amount of sunscreen only provides the square root of the SPF. So, while you may not be doubling your level of protection, an SPF 30 will block half the radiation that an SPF 15 would let through to your skin.

All sunscreen manufacturers must adhere to the exact same FDA approved tests, ensuring that the SPF claims are consistent across all sunscreens, chemical and mineral.