The biology of a smile

Look closely at a human face, and you’ll realise the mouth is a biological outlier. The rest of our skin comes equipped with a sturdy, built-in defence system. Our lips were essentially sent into the world naked.

The biology is ruthlessly simple. The skin of your cheeks is built from about 16 layers of cells. The red of your lips, the vermilion, has three to five. The tissue is so thin that the blood vessels beneath it show right through.

But the true vulnerability lies in what is missing. Lips have no sweat glands and almost no oil glands. They also have far fewer of the cells that make melanin, the skin’s own pigment. With no oil to hold in moisture and little pigment against UV light, lips live in a perpetual state of environmental crossfire.

Why do lips get dry so easily?

Thin skin is only the start. On the face, the surface cells mature into flat, tough cells that seal the skin. On the lips, they never quite finish. Dermatologists in Japan measured the lips and cheeks of 303 women. The lips lost water almost three times as fast as the cheeks — and the cheeks already lose more than most of the body. The surface of the lips held about a third as much water.

Your two lips are not equal either. In two separate studies, the lower lip held less water than the upper one. In one of them, it also lost water faster.

So lips that dry out quickly are not a personal failing. They are simply built this way.

Do lips have oil glands?

Almost none. The skin of your face is dotted with sebaceous glands, which coat it in a fine film of oil. The vermilion has no hair follicles, no sweat glands and almost no sebaceous glands. So it cannot make the sweat and oil that keep the rest of the face smooth and supple.

Even the fats between its cells are different. Lips carry fewer ceramides, the lipids that help skin hold on to water.

Why are lips red?

Three things work together. The skin is thin. A dense network of tiny blood vessels sits just beneath it. And there is less melanin in the way. In the lips there is one pigment cell for every 10 to 15 skin cells. In facial skin it is one for every four.

Lips are not all pink, of course. Depending on your skin tone, their natural colour runs from soft rose to deep brown. Researchers in Tokyo describe red lips as a uniquely human feature. They also found that the colour fades with age, as the number of blood vessels beneath the surface falls.

How do lips age?

Lips age differently from the rest of the face. They move all day — talking, sipping, chewing, smiling, kissing. Every movement folds the skin over the ring of muscle around the mouth. Young skin springs back. Over the years it loses elasticity, and the folds begin to stay.

In a study of 100 women aged 20 to 80, fine vertical lines on the upper lip became visible in the forties. The shape changes too. The upper lip grows longer, and less of the red shows. Surgeons in Freiburg found that lips do not simply lose volume with age. They lose height and elasticity, and the volume shifts.

Less melanin also leaves lips more exposed to the sun, which speeds these changes along.

Combine this exposure with the endless mechanical wear of talking, sipping and smiling, and it becomes clear why lips age on their own timeline. They don’t just weather the years — they record every movement.

They don’t just weather the years — they record every movement.

What do dry lips need?

But before you consider adopting an expressionless poker face to save your collagen, take heart. Those movements are the evidence of a life well lived.

What nature left out is oil. So the most useful thing you can give your lips is a layer of lipids that seals moisture in — the film they cannot make for themselves. Reviews of lip care point to the same answer: richer, sealing textures that slow the loss of water.

That is the idea behind our balms. Their Phyto-Lipid Complex melts onto the lips and seals in moisture, for a surface that feels soft, supple and comfortable. You will find it in the Signature Lip Kit and in Treatment to Go. The key ingredients are described on the Ingredients page.

The goal isn’t to stop smiling, eating or kissing. It is simply to give your lips what nature forgot to provide — so you can keep doing all three, with absolute impunity.

Questions, briefly

How many layers of skin are on your lips?

The red part of the lips has three to five layers of cells, against about 16 in the skin of the face. That is why the blood vessels show through.

Do lips have sweat glands?

No. The vermilion has no sweat glands and no hair follicles, and almost no oil glands. That is why it dries out faster than the skin around it.

Why is my bottom lip drier than my top lip?

In studies, the lower lip usually measures drier. It holds less water than the upper lip, and in one study it also lost water faster.