Dear Science,

My mom argues against my use of tweezers on hair, claiming that plucking hairs makes them grow back darker and thicker, while shaving hairs produces no change. I believe the opposite—shaving, not plucking, causes those icky thick black hairs; why else would my blond leg hair have turned dark after my 10-year-old experiments with razors? Who is right? (Pick me!) And why would either action affect color?

Plucker

A brief aside: Science has a deep desire to have his hair turn white before it all falls out from alopecia. Nothing quite says "distinguished scholar" like a thick (or wispy and crazy) mane of silvery strands. Think Dumbledore or Einstein. You get the picture? Great. End of aside.

Scientist Elaine Fuchs used a bit of clever genetics early in the 2000s to sort out how our bodies make hair, skin, and pigment. In the base of every strand of hair, deep in your skin, is a little bulb. Dr. Fuchs discovered in this bulb a teeny cluster of cells capable of making new skin, new oil and sweat glands, and the hair itself. These skin stem cells dutifully do their jobs throughout your life. Next time you skin your knee or elbow, peek under the bandage a few days into healing. You'll see the little islands of new skin creeping up from these little clusters of cells, filling in the lost area.

The hair strands produced by these cells are, by themselves, without pigment—the delightful gray I desire so. Melanocytes, with their own stem cells quietly sitting in this same bulb, slip little packets of protein dye into the growing hair filament. The color of your hair (and skin) is determined by the type and quantity of pigment produced by these melanocyte cells. Hair and skin can darken depending on how stimulated these become (hence, tanning). As we age, the pool of renewing melanocyte stem cells dwindles. Our hair and skin become grayed.

Unshaved hair has pleasant little tapers at either end, gracefully reaching a smooth point at the apex. When you shave, you slice the filament in its thick middle. That thickness means more pigment for the light to pass through. Hence, it appears as though your hair has become darker and thicker. Plucking rips the hair filament out of the cozy home created by the follicle, tearing the strand from the little muscle intended to pull it upright. Unfortunately, a little cluster of stem cells lives right next to this muscle. With a vigorous enough pluck, you have a chance of ripping out the hair and the stem cells. That can't be good for your future ability to heal that patch of skin. Plucking does preserve the gentle taper of hair, and thus keeps it from appearing thicker or deeper colored. Still, your correspondent suggests against it. Your mom is the more correct.

Renewingly Yours,

Science

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