What Is the Difference Between Hydrating and Moisturizing?

It can happen in the middle of winter, during a particularly dry summer, or after you’ve been scrubbing your hands or washing your face a little too vigorously: Your skin suddenly feels like it’s made of sandpaper. It becomes itchy, flaky, and dry. But is it dry or dehydrated? What’s the best way to treat it?

The two conditions are really variations on the same theme: When skin is dehydrated, it becomes dry, though you can have dry skin in general, says Sandy Skotnicki, MD, assistant professor of dermatology at the University of Toronto and author of Beyond Soap: The Real Truth About What You Are Doing to Your Skin and How to Fix It for a Beautiful, Healthy Glow.

Your Skin’s Natural Moisture

First, a little primer about moisture and the skin. “The top part of the skin is like a brick wall, meant to keep water in and dirt and bacteria out,” Skotnicki explains. She suggests that you think of your skin cells as the bricks, and the natural fats and oils in in your skin as the mortar, or glue that holds it together. When that wall isn’t working correctly, you need to repair it.  

You can develop dry skin for a number of reasons. As we reach middle age, our skin makes less sebum, the oil that keeps it soft and supple. Family history and heritage can also play a part.  Research shows that people with dark skin or very fair skin are more likely to have dry skin than those with a medium complexion. Smoking, vitamin deficiencies, and taking medications such as statins or diuretics can also lead to the problem.

The Environment vs. Your Skin

But even if you’re genetically gifted with the dewiest, healthiest skin, it can become dehydrated due to environmental causes, Skotnicki says. Not only does dehydrated skin itch, it can also show more noticeable fine lines. It can eventually lead to cracking, bleeding, and even infections.

“When indoor heating comes on in the winter, the humidity in the air decreases, and that dries out skin,” she says. Air conditioning can do the same. So can washing with too-hot water and using cleansers that have a lot of detergents.

Skotnicki points out that detergents can’t tell the difference between dirt and oil from the environment and the natural oils in your skin. Washing with harsh products -- and washing too often -- can strip away those oils. This damages your skin’s barrier and causes it to lose moisture. She recommends washing with only lukewarm water and only washing your face at the end of the day.

Continued

Moisturizing Ingredients

In addition to being gentle on your skin, you can help repair dry, dehydrated skin by adding moisturizers to your care routine. 

The term “moisturizer” was developed by advertisers and cosmetics company and has no real medical meaning. But in general, it has come to mean a product that raises water content in your skin and then locks it in. Moisturizers and hydrators cross over, depending on the types of ingredients they contain. “The two terms get kind of lumped together, but they are actually quite different,” Skotnicki says.

The two primary moisturizing ingredients are emollients and occlusives, Skotnicki says: “An emollient is something that's going to repair that brick wall, and an occlusive prevents more water from escaping.”

Emollients, which include coconut oil, palm oil, ceramides, and squalene, are lipids and oils that fill in the spaces between the skin cells. They improve the skin’s softness and make it feel smoother. Occlusives are oils and waxes that make a barrier to physically block the loss of water. They work best when you put them on damp skin. They seep into the fat cells in your skin -- the mortar in the brick wall -- to help build up the barrier. These include petrolatum (petroleum jelly), liquid paraffin, mineral oil, and lanolin.

Hydrating Ingredients

“When a product says it’s hydrating, that means it draws water into the skin, so those usually include a humectant such as hyaluronic acid or glycerin,” Skotnicki says. The molecules in humectants grab water from both the humidity in the air and from a deeper layer in the skin, and draw it to the epidermis, or top layer. 

Hyaluronic acid (HA) absorbs 1,000 times its weight in water. It’s a building block of your skin, joints, eyes, and other tissues and organs. It’s also an important part of wound healing. It  creates a protective barrier that helps the skin retain moisture. Hyaluronic acid comes in products for both the face and body.

Glycerin, also known as glycerol, is another popular humectant that has been used in hydrating creams for many years. It helps repair the skin barrier and helps skin stay supple and stretchy.

Because humectants draw water from the inner layer of the skin to the outer layer, it’s important that you combine them with occlusives to retain that water. “If you use something that's purely a humectant and you don't add an occlusive, you could actually cause more damage because you're going to suck water into the outer layer of skin. And if you haven't fixed the top part of the skin, you could actually become even drier,” Skotnicki says. “The best products will contain all three types of ingredients (emollients, occlusives, and humectants),” she says.

WebMD Feature Reviewed by Stephanie S. Gardner, MD on July 13, 2021

Sources

SOURCES:

Sandy Skotnicki, MD, assistant professor of dermatology, University of Toronto.

American Academy of Dermatology: “Dry Skin: Who Gets and Causes,” “Your Winter Skin Survival Kit.”

British Journal of Dermatology: “Glycerol and the skin: Holistic approach to its origin and functions.”

Indian Journal of Dermatology: “Moisturizers: The Slippery Road.”

Skin Pharmacology and Physiology: “Hyaluronic acid in the treatment and prevention of skin diseases: molecular biological, pharmaceutical and clinical aspects.”

DermNet NZ: “Dry Skin.”

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