Most of the time, you can thank your grandma (or rather, genetics) for those stray hairs. It’s most common in East Asian and Mediterranean ethnicities, but it can pop up anywhere. Waldorf says “if your mom or aunt had it as a younger woman, you are more likely to also.”

However, you can’t always blame mom. Sometimes facial hair is caused by hormones. If you have excessive facial hair and it’s growing in a “male” pattern (think mustache and beard), then you might have hirsuitism, which is caused by too many male hormones in your system. This is often a sign of polycystic ovary syndrome, according to Waldorf.

Kauvar adds that sometimes even your medication can cause facial hair to grow, although this is rare.