FYI: Why Do Old People Get So Hairy?

Scientists explain what causes hair to grow everywhere but the head as we age.

You’ve seen it at the local pool, at the beach, or even on your own grandpa. Old grizzled men with enough back hair to knit an afghan. Rampant tufts of hair springing out of dark nasal and ear cavities and eyebrows that look Cro-Magnon. What causes hair to grow everywhere but the head as we age?

Scientists don’t exactly know what causes hair to sprout excessively from places like the ears and nostrils but Dr. David Liebovitz, an associate professor of Medicine at Northwestern University, guesses that it has to do with hormones and the lifecycle of hair.

Hairs grow in three stages: anagen, catagen and telogen. First, hair cells grow and divide in the anagen phase. Head hair naturally remains in the anagen phase for an extended period of time, up to several years. Hair on your arms, however, will move on to the catagen phase in a matter of weeks. This is when the hair stops growing and transitions to the dormant telogen phase. The hair stops lengthening and eventually falls out naturally through shedding or external trauma such as pulling.

Liebovitz says some types of hair develop anagen sensitivity as we grow older. The long term exposure of hair follicles to hormones such as testosterone will disrupt and lengthen their growing period. That’s why nose, ear, and eyebrow hair can reach troll-doll proportions without regular trimming as we age.

Hair growth can be extremely sensitive to male hormones, according to Dr. Sarah Baker, an instructor of Dermatology at Northwestern University. “Testosterone is produced in hair follicles and different areas of hair on the body respond to testosterone differently,” Baker says. According to Baker, testosterone causes hair to grow in the beard, pubic, and underarm area, and it causes hair to shrink on the scalp, which develops into hair loss or hair thinning.

According to Dr. Liang Ma, a professor of Dermatology at Washington University at St. Louis, there’s no evidence backing up the idea that older people become excessively hairy. Body hair type and density vary across different ethnicities: “Asians have almost no body hair. Black people have curly hair and Asians have straight hair. Some isoforms in the structural form of the hair differs between ethnic groups that cause varying appearances.”

If your grandpa needs a remedy for his hairy situation, he has plenty of options. Razors, waxes and laser hair removal are all resources for those who don’t want to rock the Chewbacca look.

This story was produced in partnership with Northwestern University’s Medill School of Journalism.