May is Skin Cancer Awareness Month as 5 million cases of skin cancer are diagnosed each year in the United States. This week, Consumer Reports released its 2018 Annual Sunscreen Guide on the best sunscreens to offer protection against UV (ultraviolet) rays. They looked at 73 various sunscreen lotions, sprays and sticks, which touted 80 minutes water resistance and an SPF of 30.
The top 5 sunscreens reported are:
La Roche-Posay Anthelios 60 Melt-In Sunscreen Milk, $36 (lotion)
Equate (Walmart) Sport Lotion SPF 50, $5.00 (lotion)
BullFrog Land Sport Quik Gel SPF 50, $8.50 (lotion)
Coppertone WaterBabies SPF 50 Lotion, $9 (lotion)
Trader Joe’s SPF 50+, $6 (spray)
Sunscreens use chemicals to disperse or absorb UV rays. Inorganic compounds in sunscreen such a titanium dioxide or zinc oxide attempt to scatter the UV rays. Organic compounds such as PABA and oxybenzone attempt to absorb UV rays so they can’t damage the skin.
UVA rays penetrate deeply into both the epidermis and dermis. They can cause premature aging of the skin, wrinkles, and skin cancer.
UVB rays are shorter and primarily affect the epidermis. They are responsible for causing sunburns as well as skin cancer.
SPF stands for Sun Protection Factor. The higher the SPF, the less sun photons enter the skin and cause damage. SPF primarily measures the protection against UVB rays. We multiply the SPF factor by how long it takes one’s skin to burn by the SPF number to determine the protection factor.
In theory, an SPF of 30 suggests your skin, if it burns within 10 minutes without protection, will not burn until 300 minutes has lapsed (30 times 10). However, we find this isn’t always the case. People sweat or swim and the sunscreen dissipates. Moreover many don’t put on the proper amounts (see below.)
So instead we use SPF as a grade to how much protection the product can offer.
An SPF of 15 blocks 93% of UVB rays
An SPF of 30 blocks 97% of UVB rays
An SPF of 50 blocks 98% of UVB rays
As we see, the relationship is not linear, however the higher the SPF, the more protection we have against UV rays.
Although the SPF alludes to protection against burning, hence UVB rays, a sunscreen may still protect against both UVA rays and UVB rays if it’s a broad spectrum sunscreen.