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1. Those days in the sun catch up with you. If you sunbathe in your 20s, by your 20-year reunion, you can count on looking 10 times older than your friends who were better about sun protection, says Amy Wechsler, M.D., a dermatologist in NYC. Plus, you could wind up with uneven pigmentation, poikiloderma (which causes your neck and chest to be red, and your skin to be textured like crepe paper), brown spots, telangiectasia (visible, dilated blood vessels), and even worse, skin cancer. Be sure to wear an SPF 30 to SPF 50 365 days a year. Try Chanel UV Essentiel Complete Sunscreen UV Protection Anti-Pollution Broad Spectrum SPF 50. And if your skin is super-susceptible to burns, avoid low-cut shirts in the summer and wear a rash guard at the beach.

2. Tanning beds are no safer than the sun. The amount of UVA (the rays that cause aging) and UVB (the rays that cause burning) are higher in a tanning bed than what you'd be exposed to outside. In fact, just one time in a tanning bed (One time!) increases your risk of developing melanoma (the deadliest form of skin cancers) by 20 percent, and each additional session during the same year boosts the risk almost another 2 percent, according to a study in the British Medical Journal. Bottom line: Don't tan indoors, and always wear sunscreen when you're out and about.

3. Cigarettes age you, big time. Cigarettes damage the systems that repair your body and inhibit collagen creation, which can lead to premature fine lines and wrinkles. Puffing on cigs also dehydrates your skin because it cuts off oxygen supply, leaving skin parched and crepe-like rather than youthful and plump.

4. Acne is normal. Breakouts suck, but you're not alone: Up to 8 out of 10 of twentysomethings still get flare-ups. To stay in the clear, Dr. Wechsler suggests removing your makeup thoroughly before bed with a gentle cleanser, using a spot treatment when needed, and hydrating your face with a noncomedogenic (aka it won't break you out even more) moisturizer, like Chanel Hydra Beauty Micro Sérum, which feels light but is super-hydrating.

5. Exfoliate, exfoliate, exfoliate. Sloughing is the key to clear, glowing skin. Here's why: Since your skin cells don't shed all at once, if you skip this key step in your routine, any remaining dead cells can cause your skin to look uneven or dull. Exfoliating your face sends a signal to the cells that they should grow, making you glow. Got sensitive skin? Exfoliate every couple of days with a physical exfoliator. Then, once a week (or twice, depending on how sensitive your skin is), skip using your usual serum or moisturizer, and replace it with a leave-on chemical exfoliator, like Le Weekend De Chanel Weekly Renewing Face Care, which uses ingredients like glycolic acid to exfoliate your skin deeply, cleansing your pores of dirt, oil, bacteria, and debris, and rose water to help calm the skin as the exfoliator does its work. Always follow the application of Le Weekend with an SPF 50, since the glycolic acid it contains can make your skin sensitive to the sun.

6. Alcohol dehydrates your skin. Sorry to be a downer, but overindulging dries out your skin and will leave you looking like you're older than you are. To keep your skin plump, gorgeous, and glowing while you have a cosmopolitan, drink a glass of water after every alcoholic drink. You'll stay hydrated while having fun.

7. Sleep is sacred. Lack of rest prevents your body from rejuvenating itself, which keeps you from functioning at your peak. Sleep deprivation will also make you look older (dry skin, dark circles, a sallow complexion) and leave you irritable. "We are in a constant state of damage and repair," Dr. Wechsler says. "We heal and grow in our sleep, when our stress hormones are at their lowest and the molecules that repair skin are the highest." Aim for eight hours — it's called beauty sleep for a reason.

8. Skip shaving before a pedicure. Shaving can cause tiny nicks in your skin, leaving you susceptible to bacteria and infection. And since basins at nail salons are often not cleaned with bleach until the end of the day, you're at risk of bacteria entering those tiny openings in your skin once your nail tech turns on the jets. It's also smart to be the first client at the salon in the morning to ensure the basins are clean. Or choose a salon with individual basins you know get cleaned after each use.

Model: Clair Westenberg

Makeup: Colleen O'Neill

Hair: Ryan Trygstad

Stylist: Brandy Joy Smith

Clothing credits: Lolita Silk Robe, JOSIE NATORI

Location: The Standard, High Line

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Carly Cardellino

Carly Cardellino was the beauty director at Cosmopolitan. If you follow her Instagram, then you know she'll try just about any beauty trend or treatment once (the pics of her purple hair are on IG to prove it). But her favorite part about being in beauty is finding the most effective products, and then sharing that intel with others—because who wants to spend money on stuff that doesn't work? No one, that's who. Her most recent discovery: De La Cruz Sulfur Ointment, which will change your blemish-clearing game! Hopefully through the beauty stories she writes—and the experiences she shares—you can see exactly why she's in this business.