It's one thing to know, in an abstract sense, that smoking damages skin, but it's quite another to look at two identical faces and directly compare the differences when one twin is a heavy smoker and the other, a light smoker — and in some cases, one smokes while the other has totally abstained. In both cases, the results are startling. You're able to see profound effects, not only around the lips and mouth like you would expect, but also around the eyes.
Of course, this study is informal. It doesn't correct for other lifestyle imbalances — whether one twin drinks more alcohol or exercises less, but it's unsettling nevertheless.