You learned this in sixth grade science: the skin is the human body’s largest organ, and more than half of your body is made of water. How are these facts related? Skin provides a barrier that helps regulate just how much water gets in (and out). To do this properly, our skin needs both water and oils — we’ll call that hydration and moisture, respectively.

In skincare terms, moisturizing typically means the act of applying a product that combines humectant, emollient, and occlusive ingredients. We’ll explain what those are, how they’re important for skin health, and exactly why you need to moisturize to keep your skin healthy and glowing.

How does skin get dry?

Our skin is incredibly complex, designed to maintain its delicate balance in order to function optimally. But especially overnight, our skin becomes dehydrated through a process called transepidermal water loss (TEWL). Add in modern life — that late night out, an overzealous exfoliating session, even just the changing seasons — and skin’s equilibrium is easily thrown off.

This can cause the tightly-organized cells on the very top layer of our skin — the stratum corneum — to shrink and become brittle. Flakes, fine lines and fissures form, giving skin that characteristic “dry” look.

Is having dry skin bad for you?

When the stratum corneum dries out, microscopic openings make skin more prone to toxins, bacteria and other outside invaders that can affect skin health. The result is uncomfortable, tight-feeling, flaky skin that is much more prone to a variety of skin concerns — including shedding, premature aging, and acne.

Does dry skin cause aging?

It’s true: dry skin looks older. For the most part, a lack of hydration and moisture doesn’t cause aging, per se — it mainly accentuates the fine lines and wrinkles already there. 

It’s worth noting, however, that dry, damaged skin is more prone to the processes and elements that do cause aging. Chronic inflammation can affect things like collagen production, leading to more sagging and wrinkling.

Fortunately, the reverse is also true: properly hydrated and moisturized skin looks healthier and younger, because it’s plump and smooth.

What should I look for in a moisturizer?

As noted earlier, moisturizers typically contain a combination of ingredient types:

• Humectants: draw and bind water into skin, including glycerin, hyaluronic acid, and beta glucan.
• Emollients: fill in the gaps between skin cells, including squalane and ceramides. 
• Occlusives: form a barrier to seal in moisture, including petrolatum, castor oil, and shea butter.

The most effective moisturizers combine ingredients from these categories, without causing breakouts. Look for phrases like “for acne-prone skin,” “won’t clog pores,” or “non-comedogenic formula” on the label. Try: SLMD Dual Defender (AM) and Facial Moisturizer (PM).

Do I need moisturizer if I have oily skin?

We’ve covered this topic in depth here, but it’s worth repeating. Though it may sound counterintuitive to add moisture to skin that is already oily and acne-prone, having oily skin doesn’t mean it’s properly hydrated. In fact, you can have a complexion that’s both oily and dry, and dry skin can actually make acne and breakouts much worse.

"There is some belief out there that if you have oily skin, you don’t need to or even shouldn’t moisturize,” says Dr. Sandra Lee (aka Dr. Pimple Popper). “This is NOT true - ALL skin types need moisturizer. However, if you have oily skin, you should be more selective about what moisturizer you’re using.”

If you have acne, it’s important to apply moisturizer because treatment ingredients like benzoyl peroxide can be very drying — that’s why Dr. Lee’s SLMD Acne System includes a moisturizer.

Avoid heavy, occlusive products like Vaseline and opt for lightweight moisturizers that will let your skin breathe, like SLMD Facial Moisturizer. If your skin still seems dry, or could use a bit of plumping, add a humectant. SLMD Hyaluronic Acid Serum also contains squalane, so it hydrates and locks in moisture.