Jun 26, 2017
In brief, according to the folks at badgerbalm.com we find out about protection from the sun and what SPF really means. It's critical to protect your skin from sun damage because it can lead to something serious later on.
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.
Dermatologists recommend using a SPF15 or SPF30 sunscreen. Higher SPFs don't give much more protection.
What is SPF Sunscreen?
SPF, or Sun Protection Factor,is a measure of how well a sunscreen will protect skin from UVB rays, the kind of radiation that causes sunburn, damages skin, and can contribute to skin cancer.
If your skin would normally burn after 10 minutes in the sun, applying an SPF 15 sunscreen would allow you to stay in the sun without burning for approximately 150 minutes (a factor of 15 times longer). This is a rough estimate that depends on skin type, intensity of sunlight and amount of sunscreen used. SPF is actually a measure of protection from amount of UVB exposure and it is not meant to help you determine duration of exposure.
For best protection, experts recommend using a minimum SPF sunscreen of 15, applying the proper amount (2mg/cm2 of skin, or about one ounce for full body coverage), and reapplying every 2 hours.
Most people under-apply sunscreens, using ¼ to ½ the amount required. Using half the required amount of sunscreen only provides the square root of the SPF. So, a half application of an SPF 30 sunscreen only provides an effective SPF of 5.5!
What is SPF Sunscreen?
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, another way of looking at it is:
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.
What is SPF sun protection factor?
It’s complicated, but to keep it simple, most dermatologists recommend using a SPF 15 or SPF 30 sunscreen.
Why not use a really high Sun Protection Factor? Sunscreens with really high SPFs, such as SPF 75 or SPF 100, do not offer significantly greater protection than SPF 30 and mislead people into thinking they have more protection than they actually do. Additionally, in order to have broad spectrum protection, the UVA protection should be at least 1/3 of the UVB protection. High SPF sunscreens usually offer far greater UVB than UVA protection, thus offering a false sense of full protection.
SPF Sunscreen Testing
All sunscreens must undergo FDA approved SPF testing in order to make a UVB 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).
Image: Sunscreen - clipartpanda.com
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