You've seen the letters on every bottle of sunscreen. But what do they stand for? What do they mean?
SPF stands for Sun Protection Factor and it's a measure of how much protection a sunscreen provides against the sun’s UVB rays.
UVB rays are one of the two types of UV rays that can damage our skin. UVB rays hit the outer layer of your skin, called the epidermis. According to the American Academy of Dermatology, these rays cause sunburn and are heavily linked to skin cancer. The other type is called UVA rays, and these rays reach the middle layer of your skin. They primarily cause tans, which are the side effect of damage that causes your skin to age prematurely. For this reason, broad-spectrum sunscreen is recommended, as it protects you from both UVB and UVA rays.
The higher the SPF number is, the higher the amount of protection you get from it. For example, if you wear SPF 15, your skin absorbs 15 times fewer UVB rays than it would without sunscreen on. Ideally, this would mean that it would take 15 times longer to get a sunburn while wearing SPF 15, but that's not necessarily the case. The intensity of sun exposure varies throughout the day, which can change the amount of time you’re protected. Also, moisture from sweat and water can cause sunscreen to wear off far earlier than you expect, so make sure you reapply every 2 hours to stay protected.
Dermatologists recommend SPF 30 because it filters out 97% of UVB rays. Higher SPFs such as 50, 70 and 100 will block slightly more UVB rays, but it is important to note that no sunscreen will give you 100% protection.
No matter which SPF you use, be sure to apply the directed amount half an hour before going in the sun, and reapply every 2 hours. This will help you get the best possible protection from your sunscreen.