I spent six years studying the statistical mechanics of supercooled fluids and electrolyte solutions. Alas, my highbrow research was insufficient to net me a faculty position at a top university. A man by the name of Mark Tarnopolsky found a more successful route. In the study of his that caught my eye (via The New York Times via A Reader Referral), he gathered together a small group of sedentary elderly adults from whom “skin samples were acquired from the upper portion of the non-sun-exposed buttocks below the waistline using a 4-mm punch biopsy.” When you hear “elderly,” “sedentary,” and “biopsy” in one sentence you probably assume he’s studying cancer. But no. He’s cutting off chunks of people’s butt-skin to find out what makes old butts look so old.
Let’s back up. Apparently the outermost layer of our skin is called the stratum corneum. Prof. Tarnopolsky found (I think other people also found this before him, but his data confirm it) in a group of 29 20- to 84-year-olds that as people age their stratum corneum gets thicker. At every age, people who get over four hours of aerobic exercise per week have a thinner stratum corneum than people who get lass than one hour of aerobic exercise per week. In fact, the exercisers over 65 were indistinguishable from non-exercisers in their twenties and thirties. He did not find any difference in loss of collagen between exercisers and non-exercisers.
This observational result needs to be checked with an experiment. Prof. Tarnopolsky did sort-of that. He took ten
flabby old people sedentary elderly adults and assigned them to do aerobic exercise (moderate running or cycling for 30 minutes twice per week) for three months. He did not use a control group. At the end of three months he asked them yet again to drop trow for a skin biopsy. It turned out their stratum corneum had gotten as thin as that of the sedentary twenty- and thirty-somethings and their collagen content had gone up.
Sadly, this study was one of Prof. Tarnopolsky’s lower cited papers and although it was published in 2014 it doesn’t appear to have been replicated by anyone else. So this small, short-term, uncontrolled trial is the best we have to go on when maintaining our butt-skin. This research nicely complements the much larger, longer, controlled trial on sunscreen. The sunscreen-and-skin-aging study excluded people over 55 because the principal investigator speculated that over 55 everyone’s skin deteriorates even if they use sunscreen. This study biopsied butt-skin as a way of controlling for sun damage. If you are a future 84-year-old, have no fear! You too can have the butt-skin of a lazy 30-year-old, if only you exercise and use sunscreen your whole life.