Since we’re right in the middle of a hot summer, there’s no better time to re-examine the age-old topic of sunscreen. Here, New York City dermatologist and self-proclaimed sunscreen fanatic, Marnie Nussbaum, MD—a go-to for models during fashion week—breaks down everything you’ve ever wanted to know about SPF.
Do I really need to wear sunscreen every day?
Absolutely! Rain or shine, hot or cold weather… we must wear sunscreen daily, as the UV rays that cause skin cancer and ageing are present regardless of temperature and even clouds. Both UVA and UVB rays contribute to skin cancer formation. UVA rays penetrate deeper and are also the cause of premature ageing and skin breakdown, while UVB rays are shorter in wavelength and cause the skin to burn. UVA rays even penetrate windows; therefore, even if you are driving or sitting at a desk all day, you may be exposed to harmful UV rays. UVA rays remain at relatively the same level all day, while UVB rays peak midday. Even if you are running around doing errands all day, your incidental sun damage truly adds up!
Does sunscreen expire?
In general, most sunscreens have an expiration date and should absolutely not be used past that date (usually three years from manufacturing). However, many factors may make the sunscreen less potent than originally intended, including heat exposure (leaving it by the pool or in hot cars, etc). Chemical sunscreens usually have ingredients like oxybenzone and avobenzone that can oxidise and become less effective over time. Mineral sunscreens that contain zinc or titanium are usually more stable, but the formulation can degrade over time, causing separation of ingredients and causing the lotion to become grainy or watery and, therefore, not properly effective. Furthermore, frequent opening and closing of the bottle can allow for bacteria build-up within the lotion, wreaking havoc on skin. If you are using sunscreen properly (daily and reapplying every two hours), you should be going through bottles way before the expiration date. If it has been over a year with the same sunscreen, you are not using enough!
How often should you replace your sunscreen?
If a summer has gone by and you are not finished with a bottle of sunscreen, you are not applying it as frequently or as generously as recommended! I recommend a tablespoon for the face and a full shot glass for the body every two hours, or more frequently if you swim or sweat (even if it says it’s water-resistant). You should not see any changes in consistency. If you see clumping or graininess, the sunscreen is likely not at its intended potency. Also, if a bottle begins to smell funny, it may be a sign of bacterial contamination. When in doubt, replace.
What’s the difference between SPF 50 and SPF 75?
SPF is a number that says the time it would take for the sun’s UVB radiation to cause redness to the skin when using the sunscreen exactly as directed versus the time it would take without any sunscreen. Therefore, in a perfect world, SPF 30 means it would take 30 times longer for the skin to burn than compared to not using anything. However, very rarely is sunscreen used exactly as directed. Also, genetics vary, therefore, someone may need much more than SPF 30 for protection versus another person. Studies have shown that people get a false sense of security when using higher SPFs and stay in the sun much longer and rarely reapply. Most dermatologists recommend everyone use at least SPF 30 or higher. It should be applied 30 minutes prior to going outside and reapplied every two hours or sooner if swimming or sweating. Lastly, SPF numbers are not linear; meaning, SPF 100 is not double the protection of SPF 50. Sunscreens with an SPF of 30 protect against 97 percent of UVB rays while SPF 45 protects against 98 percent. To note, SPF only refers to UVB protection, not UVA. Therefore, always look for a sunscreen that says broad-spectrum (protects against both UVA and UVB rays).
How much SPF do you recommend for everyday use during the summer?
I always recommend at least SPF 30 or above on all exposed areas, including the face, neck, chest, hands, and tops of ears.
After how many hours should you reapply?
“Every two hours, but sooner if you swim or you sweat (even if the product says it’s water-resistant). Of note, absolutely nothing is waterproof, and products are no longer able to be labeled as such.”
What’s the most commonly forgotten area to apply sunscreen?
The tops of ears, tops of hands, and tops of feet. I also recommend lip balms with SPF as well as hats to protect the scalp (lots of skin cancers in both young and old people hide under the hair).
What should you do if you get a sunburn?
Your risk of melanoma doubles if you have had more than five sunburns! Therefore, avoid them at all costs. However, nobody is perfect, and they happen. Immediately cool the skin with cold damp towels or a cool shower (do not directly apply ice). Use a soothing moisturiser with aloe to calm the skin (nothing thick with petrolatum, or greasy, which can trap the heat, worsening the burn). Immediately take a non-steroidal anti-inflammatory (NSAID), such as ibuprofen, to calm the inflammation. An over-the-counter hydrocortisone one-percent cream may additionally help calm the skin (can be used twice daily). Drink lots of water and fluids to replenish your body’s moisture and electrolytes. If you or a child has any fevers, chills, or blisters, or seems confused, immediately seek medical attention.
This article originally appeared on Vogue.com
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