Why do lips get so chapped in winter?

You get ready to leave the cozy warmth of your house and brace for the winter's harsh weather — and, of course, you can't step foot outside without pocketing your trusted lip balm.

But have you ever wondered why your lips get dry in the winter?

The answer lies in lips' unique anatomy, Dr. Luke Powles, a London-based physician and associate clinical director for Bupa Health Clinics, told Live Science in an email. "The skin on your lips has a thinner protective barrier compared to the rest of the skin on your face, which makes it more susceptible to dehydration," he said.

Starting at the "vermillion border" — the often-sharp line that demarcates lip tissue from the rest of the face — the tissue resembles the mucous membrane that lines the inside of the mouth. It consists of only three to five layers of tissue and does not contain any of the hair follicles or sweat glands found elsewhere on the face, according to the medical resource StatPearls.

Related: Can lip balm make your chapped lips worse?

In fact, "the cellular layers of skin on your face are up to six times thicker than found on your lips," Powles said. "Your lips also have fewer oil glands compared to other parts of the body."

This comes into play during the winter, when the air outside gets colder and less humid and people switch on the heat in their homes and businesses. This continuous exposure to dry air dehydrates the delicate skin of the lips, causing it to crack, peel and bleed — a condition scientifically known as common cheilitis, Powles said.

While it's tempting to try to ease the discomfort of common cheilitis by licking your lips — and we sometimes do this without thinking — this may actually aggravate the problem. That's because saliva contains digestive enzymes, such as amylase, which breaks down starches into sugars, and lipase, which aids the digestion of fats.

"When you lick your lips, the dried saliva removes the natural oily protective layer that helps keep your lips healthy," Powles said. Over time, these enzymes can damage the lip skin itself and contribute to dehydration.

Having a stuffy nose — a hallmark of the winter cold and flu season — can also expose the lips to excess saliva by forcing a person to breathe through their mouth, according to a 2020 review in the International Journal of Women's Dermatology.

Dry lips are not only an aesthetic issue but also a medical one. For example, chapping can leave lip skin more prone to infections that penetrate the skin barrier, Nina Prisk, an aesthetics nurse prescriber at Update Aesthetics clinic in London, told Live Science by email. Microbes such as the bacterium Staphylococcus aureus or yeast Candida albicans can fuel inflammation in the lips and thus aggravate the symptoms of cheilitis, according to a 2018 review published in the journal Acta Clinica Croatica.

If your chapped lips don't improve when you use lip balms, ointments or a humidifier, it may be worth speaking with a medical provider about more advanced treatments, Cleveland Clinic advises.

This article is for informational purposes only and is not meant to offer medical advice.

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