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.