Smoking causes wrinkles by upsetting the body's mechanism for renewing skin. Dermatologists say the finding confirms the long-held view that smoking ages skin prematurely. Skin stays healthy and young-looking because of a fine balance between two processes that are constantly at work.

The first breaks down old skin while the second makes new skin. The body breaks down the old skin with enzymes called matrix metalloproteinases, or MMPs. They chop up the fibers that form collagen -- the connective tissue that makes up around 80 per cent of normal skin.

Researchers suspected that smoking disrupted the body's natural process of breaking down old skin and renewing it. To test their idea, they first made a solution of cigarette smoke by pumping smoke through a saline solution. Smoke was sucked from cigarettes for two seconds every minute. Tiny drops of this smoke solution were added to dishes of human fibroblasts, the skin cells that produce collagen.

After a day in contact with smoke solution, the researchers tested the skin cells to see how much collagen-degrading MMP they were making and they found that cells exposed to cigarette smoke had produced far more MMP than normal skin cells.

They also tested the skin cells to see how much new collagen they were producing and found that the smoke caused a drop in the production of fresh collagen by up to 40 per cent. This combined effect of degrading collagen more rapidly and producing less new collagen is probably what causes premature skin ageing in smokers. In both cases, the more concentrated the smoke solution the greater the effect on collagen.

Archives of Dermatological Research April 2000 292:188