It seems like sunscreen has always been around, to protect your skin, keep you safe from UV radiation, and prevent signs of aging. But despite our familiarity with sunscreen, one thing remains a mystery for many: what is SPF?
SPF measures sunscreen protection from UVB rays, the kind that cause sunburn and contribute to skin cancer. SPF does not measure how well a sunscreen will protect from UVA rays, which are also damaging and dangerous.
What Do the Numbers Mean?
According to AAD, it is recommended to use sunscreen with a sun protection factor (SPF) of at least 30, which blocks 97 percent of the sun's UVB rays. Higher number SPFs block slightly more of the sun's UVB rays, but no sunscreen can block 100 percent of the sun's UVB rays 1 .
You might think that selecting SPF 100 over SPF 15 is a smart move. But knowing how these numbers work is more important when it comes to sun safety. It is not always an exact science, but a sunscreen with SPF 15 should keep you safe in the sun and prevent burning 15 times longer than with unprotected skin. This means that SPF 30 sunscreen should extend this time 30 times. This number will be different for every person. If you can go out into the sun with no SPF on for 10 minutes before you start to see a color change on your skin it means an SPF of 15 will be effective for 150 minutes (10 x 15), if applied correctly and if the adequate amount was used. But again, this is not an exact science.
Outdoor Wear vs. Indoor Wear
If you're inside most of the day with just short intervals in the sun, going out to your car in the morning, walking into the office and then back again at the end of the day, you can use a sunscreen or cosmetic product with an SPF of 15 or higher. If you spend a lot of time outdoors, especially when and where the sun is strongest, the beach, golf course or tennis court, you need an SPF 30 or higher, water-resistant sunscreen.
A common question is "isn't the SPF in my make-up enough"? It is best to think of the sunscreen in your moisturizer, BB or CC cream, foundation, or other cosmetics just a bonus. Most users do not apply these products in the quantity necessary to create meaningful protection. Additionally, the sunscreen in most of these products is not considered broad spectrum, so it is not providing the same coverage as your usual sunscreen.
It is also important to remember that high-number SPFs last the same amount of time as low-number SPFs. A high-number SPF does not allow you to spend additional time outdoors without reapplication. Sunscreens should be reapplied approximately every two hours when outdoors, even on cloudy days, and after swimming or sweating, according to the directions on the bottle 1.
Need to Know
As an FDA-regulated product, sunscreens must pass certain tests before they are sold. But how you use this product, and what other protective measures you take, make a difference in how well you are able to protect yourself and your family from sunburn, skin cancer, early skin aging and other risks of overexposure to the sun. Some key sun safety tips include:
- Limit time in the sun, especially between the hours of 10 a.m. and 2 p.m., when the sun's rays are most intense.
- Wear clothing to cover skin exposed to the sun, such as long-sleeved shirts, pants, sunglasses, and broad-brimmed hats.
- Use broad spectrum sunscreens with SPF values of 15 or higher regularly and as directed.
- Reapply sunscreen at least every two hours, and more often if you are sweating or jumping in and out of the water 2.