The premise of slugging—a name inspired by the viscous texture of snail mucous—is simple: By applying an occlusive agent as the last step of your nighttime beauty routine, you strengthen the skin’s barrier and trap in hydration. “It’s something we’ve always done in dermatology,” says Montreal-based dermatologist Loukia Mitsos. “When the skin is dry, it lacks intercellular lipids, which form a kind of glue to hold the skin cells together; without this support, the skin barrier is defective. With slugging, we moisturize and relipidate the skin to regenerate its barrier, which becomes waterproof again and can prevent the loss of transepidermal water.” To properly slug, apply a serum or moisturizer that contains humectants (which attract water), such as hyaluronic acid or aloe vera, to clean skin before spreading on a pea-size amount of an occlusive agent, such as petroleum jelly (a.k.a. Vaseline, which is a by-product of crude-oil refining and therefore helps in the recovery of waste) or an ointment, in a thin layer. In the morning, cleanse your face with a mild soap and see how your skin has responded to the treatment. This technique can be repeated until any feeling of tightness is eliminated or once a week as a preventative measure.

However, it’s important to not use certain active ingredients on slugging nights, warns Mitsos. “The absorption of all the care applied under the occlusive is amplified, so you should avoid active ingredients such as AHA and BHA acids and retinoids, which can dry out the skin even more and cause irritation.” Another downside: Although it does wonders for dry skin and eczema, the technique is not recommended for oily skin. Even though petroleum jelly does not clog pores (its molecules are too large to penetrate the skin), the waterproof film it forms on the epidermis does not allow natural oils to escape, which can irritate hair follicles and cause acne. And if the dubious reputation of petroleum jelly is still worrisome, let Mitsos reassure you. “It’s recommended by the American Academy of Dermatology,” she says. “It is commonly used as a treatment for irritation, burns and even diaper rash on babies. It is the most accepted inert substance to use on skin that’s allergic to multiple components.” If you’re interested in the slugging technique but still prefer to avoid petroleum jelly, opt for thicker night creams or oils instead.

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