Why lips chap
in winter.

Every year, somewhere around the first hard frost, lips start splitting. It is easy to blame the cold, and the cold is involved, but the mechanism is mostly about how much water the air around you can hold.

Cold air holds less moisture. Warm air can carry a lot of water vapour; cold air carries much less. So outdoor air in January is dry in absolute terms even when it feels damp, and dry air pulls water out of any wet surface it touches — including your lips.

Indoor heating makes it worse, not better. Take that cold outdoor air, bring it inside and heat it to twenty degrees, and its relative humidity collapses. A heated room in midwinter can sit at fifteen or twenty per cent humidity, which is drier than a lot of deserts. You spend most of the winter in that, not outside in it.

Lips are badly equipped for this. The skin on your lips has no oil glands and a much thinner outer layer than the skin around them, so it has neither the sebum nor the barrier thickness that the rest of your face uses to hold water in. It loses moisture several times faster than cheek skin and has nothing of its own to replace it with.

And then there is licking. It is the single most effective way to make the problem worse, and it feels like relief, which is why everybody does it. Saliva evaporates within seconds and takes surface moisture with it, so each lick leaves your lips drier than before. It also contains digestive enzymes that are not kind to thin skin over repeated exposure.

Breathing through your mouth does the same thing more slowly, which is why a week with a blocked nose wrecks your lips.

What actually helps. A humidifier in the room you sleep in, which addresses the cause rather than the symptom. An occlusive balm applied before going out and before bed, not after the splitting starts. Water, since no balm fixes dehydration from the outside. And a scarf over your mouth in real cold, which sounds fussy and works.

When it is not just winter. Cracking at the corners of the mouth specifically, lips that bleed, or chapping that does not improve over a few weeks is worth showing to a pharmacist or a doctor. Angular cheilitis, a B-vitamin deficiency and contact allergy all present as stubbornly dry lips and none of them is solved by another tin.

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