A Dermatologist Answers Our Questions on Better Sun Safety

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Photo: Corbis

Welcome to sunscreen week at the Cut, where we provide you products reviews, tips, and news you'll need for sun safety. But first, here's this: Protecting your skin from harmful UVA/UVB rays is the best beauty tip. Ever.

A few weeks ago, the Cut staff sent a slew of SPF, sunscreen, and sun-damage questions to New York–based dermatologist Dr. Heidi Waldorf of Mount Sinai Hospital. Below, her take on the best SPF numbers, waterproof sunscreen, and whether freckles are a warning sign for sun damage. Check back on Friday, when we'll publish the second part of the Q&A.

What’s the highest SPF that’s actually effective?  
The more important question is what's the lowest that is effective? SPF rates protection against UVB, the short wave "burning" rays. For protection against UVA, the long wave deeper penetrating "aging" rays, other tests are used. The best UVA protective ingredients available in the USA are zinc oxide, titanium oxide, avobenzone, and mexoryl SX. The newest FDA guidelines define a product with SPF 15 that also passes specific UVA tests (defining it as "broad spectrum") as the lowest SPF that can reduce the risk of skin cancer and premature aging. Below SPF 15, sunscreens will be able to be labeled "broad spectrum" if they pass the UVA tests, but not be able to be labeled as "reducing sun damage." The highest SPF labeling will be SPF 50+, because over that number there are incrementally limiting returns in added UVB protection. The key is that higher SPF products aren't dangerous — they just may give users a false sense of security. Using the higher SPF product gives longer protection against sunburn but not an equal amount of protection against the deeper tanning rays, so patients may remain outdoors longer without reapplying sun protection or seeking shade. I use the analogy of having a car with all the safety bells and whistles: You still shouldn't drive at 90 mph on an icy road. Patients frequently tell me they used SPF 100 on vacation and "couldn't help" getting tan. I can come home from a sunny outdoor vacation having used SPF 30 without changing color because I apply it well at the start of the day, then reapply hourly and have the added protection of hats and clothing whenever possible.

A friend tried to convince me that there's no difference between SPF 30 and SPF 50 because what matters more is how often and generously you apply. Is this true? 
I agree with your friend. Although, if you use the same amount of each and reapply similarly, the SPF 50 will be incrementally better [see above question]; you can do just as well with an SPF 30 applied generously and reapplied frequently.

Is waterproof sunscreen actually waterproof after you get out of the water or should you reapply? Does it make a difference if you’re in salt or chlorine water? 
No sunscreen is fully waterproof and none can last "all day." The new guidelines will define water resistance as being for 40 or 80 minutes, based on the way it is tested. It is important to reapply sunscreen within the first hour outdoors, every one to three hours, and after swimming (salt, fresh, or pool water), sweating, or toweling off. 

How long does it technically take for sunscreen to be applied properly? 
It's generally recommended that sunscreens with chemical sunscreen ingredients be applied at least 30 minutes before sun exposure. I recommend applying any sunscreen right after showering, before getting dressed, to avoid skipping areas as clothing shifts. Apply to any area that might be exposed and rub in well. Physical (mineral) sunscreen ingredients rub in best using a straight, not circular, motion. And since it is difficult to rub in the entire amount you need all at once, I recommend applying half the amount first then the second half after the first has absorbed.

Does it mean I’m prone to more sun damage if I have more freckles?
Fairer skinned individuals, like those prone to freckling, are more prone to skin cancer and premature aging because they have less intrinsic SPF from melanin [the molecules that determine our skin color; the darker it is, the more UV protection it naturally offers].

What’s the safest to tan? Like, for those patients who want a true sun-tanned look without self-tanners? 
There is NO safe way to develop an ultraviolet-induced tan. By definition, a tan is [skin] damage. Think of tanning leather! The only way is to use self-tanners.