A day at the beach is incomplete without the sticky feel of sunscreen leaving white streaks across your cheeks. We wear it because we know we have to. Dermatologists and our mothers alike have instilled into our brains the need for a high SPF sunscreen since before we could walk. But what exactly does having a “high SPF” sunscreen entail?
The SPF on sunscreen stands for sun protection factor, a relative measurement for the amount of time the sunscreen will protect you from ultraviolet (UV) rays. UVB rays primarily affect the outer layer of the skin, the epidermis. They are responsible for sunburns and some surface-level skin cancers. The sun also emits UVA rays, which can penetrate into the lower level of the skin, called the dermis. UVA rays are typically associated with “tanning.” However, the darker color of the skin is a sign of damage to cells in the dermis. SPF numbers typically refer only to UVB rays, but some sunscreens can protect against UVA as well.
The SPF (Sun Protection Factor) scale is not linear:
• SPF 15 blocks 93% of UVB rays
• SPF 30 blocks 97% of UVB rays
• SPF 50 blocks 98% of UVB rays
So, one way of looking at this is that SPF 30 sunscreen only gives you 4% more protection than SPF 15 sunscreen. Or:
• SPF 15 (93% protection) allows 7 out of 100 photons through
• SPF 30 (97% protection) allows 3 out of 100 photons through.
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. It’s complicated, but to keep it simple, most dermatologists recommend using a SPF 30 or higher.
How does the SPF tell you how long you’re protected for? Well, let’s say you typically burn after being outside for 30 minutes and have an SPF 15 sunscreen you plan to use. You’d multiply 30 by the SPF, in this case 15. That means that you’re technically protected for 450 minutes, or 7.5 hours—do note that this is technically speaking. Most sunscreens will wear off long before then from exposure to the elements as well as improper application. It is recommended that you reapply every two hours. The number of UVB rays you’re protected from also increases with SPF, though marginally. SPF 15 blocks 93% of UVB rays, SPF 30 blocks 97%, and SPF 100 blocks 99%.
SPF Sunscreen Testing
All sunscreens must undergo FDA approved testing in order to make a SPF claim. There are three main types of SPF testing; SPF Static, SPF Water Resistant 40 Minutes, and SPF Water Resistant 80 Minutes. 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. All SPF testing is conducted in vivo (with human subjects). Badger sunscreens are tested according to the FDA monograph, Colipa (EU), and Australian requirements.
The Facts about SPF
The SPF number tells how long the solar radiation will take to affect your skin. For example, SPF 50 take 50 times longer to affect your skin if you weren’t using sunscreen. For example, if you normally burn your skin after 20 minutes of sun exposure, but you are wearing SPF 50, then you multiply 20×50. This will give you 1000 minutes of protection. But this is not completely accurate. This is why you need to reapply every couple of hours, especially if you are out during the summer.
The higher the SPF, the more time you can be exposed to the sun without causing you any harm. If you are planning an outdoor activity, choose at least SPF 30 and reapply every two hours. However, not all products are the same. Consider your skin phototype and the type of activity you will do. For example, if you are planning to go to the beach or pool choose a waterproof and broad-spectrum product.
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