Thin lips

Lip volume is largely inherited. Genes set the height of the vermilion, the pink part of the lip, how sharply its border is drawn, and how far the lip projects forward. Naturally thin lips are simply one anatomical variation among many, not a sign of damage or aging. They do, however, carry less reserve, so age-related changes can show sooner.

Collagen is the protein scaffolding that keeps the lip firm, and hyaluronic acid is the molecule that binds water inside it, like a sponge. Collagen production declines from the mid-twenties at roughly 1% per year, and skin hyaluronic acid starts falling in the twenties, with significant loss after 40. With less scaffolding and less water, the lip deflates and fine vertical lines settle in.

Lips rest on the teeth, the jawbone and the soft tissue behind them, the way fabric rests on a frame. With age, this underlying support gradually recedes and the area around the mouth loses volume. With less to project against, the upper lip lengthens and rolls slightly inward, so less of the pink lip stays visible at rest.

Lips face the sun head-on and contain very little melanin, the natural pigment that filters UV elsewhere on the skin, so they take that exposure almost unshielded. UV light breaks down collagen and elastin fibres, and photoaging accounts for roughly 80 to 90% of visible skin aging. Unprotected lips therefore thin, dry and line earlier than they otherwise would.

Smoking accelerates lip thinning twice over: the chemicals in smoke degrade collagen, and the repeated pursing motion folds the skin around the mouth in the same place thousands of times. Drinking through straws and other habitual pursing add similar creasing. Each fold matters more here than elsewhere, because lip skin is so thin it has little support to bounce back with.