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Sunscreens, UVA and UVB

I took this from a journal called The Prescriber’s Letter. It discusses a few of the things to be considered when buying a sun screen.
A new sunscreen called Mexoryl SX will raise questions about optimal sunscreen protection.
SPF is often misunderstood. SPF applies only to UVB…not UVA. UVB causes the familiar sunburn. Explain that SPF is an estimate of how long a person can stay in the sun without obvious sunburn.
For example, if a person would burn in 10 minutes with NO protection, then an SPF 15 sunscreen will protect 15 times longer or 150 minutes…and an SPF 30 would protect 30 times longer or 300 minutes.
Tell patients there’s no proof that an SPF over 50 gives any measurable added benefit.
UVB ratings get the most attention, but are only part of the story.
UVA ratings will appear on some sunscreens. You’ll see 1, 2, 3, or 4 stars indicating low, medium, high, or highest protection.
UVA causes skin aging and skin cancer…not visual sunburn.
For now, recommend sunscreens labeled broad-spectrum. These contain UVA blockers such as avobenzone, zinc oxide, and/or titanium.
You’ll now see Mexoryl SX (ecamsule) in some Anthelios sunscreens. Mexoryl SX covers some of the shorter UVA rays that are not covered by avobenzone…and it’s more stable in sunlight.
But when avobenzone is combined with octocrylene, oxybenzone, or other ingredients it’s more stable and has a broader spectrum.
Recommend zinc oxide or titanium dioxide for sensitive skin. They block UVA and UVB by sitting on top of the skin…not binding to it.
Water resistance ratings refer to how long the product is effective during swimming, heavy sweating, etc.
Explain that a product labeled “water-resistant” lasts about 40 mins in water…and a “very water-resistant” product lasts about 80 mins.
Proper application is key. Instruct people to apply sunscreen 20 minutes before sun exposure…and reapply at least every 2 hours.
Emphasize applying enough…about 1/2 to one teaspoon per body part (leg, arm, back, face, etc)…or about 1 ounce for the full body. Applying only half the amount will give only half the protection.
Advise avoiding sunscreen/insect repellent combos. Suggest using separate products because the sunscreen needs to be applied more often than the repellent. Advise patients to apply the sunscreen first, then the repellent.
Drug-induced photosensitivity is primarily due to UVA rays.
Advise patients taking photosensitizing drugs to use a broad-spectrum sunscreen.