As it turns out, the "random" hairs you find in places like your chin actually aren't so random. If you ever find a stray hair on your body in a place you've never seen one before, it's likely due to a hormonal change. "Stray hairs occur in different age groups for different reasons," dermatologist Orit Markowitz, MD, told POPSUGAR. "As women become perimenopausal or menopausal, unwanted facial hair is common due to hormonal changes."
During menopause, your body will start producing less estrogen while still producing the the same amounts of testosterone (this also happens when you ovulate). That testosterone can, in turn, cause you to grow unwanted facial hair in places like your upper lip, chin, or neck.
Outside of things like ovulation and menopause, though, women can also begin to see facial hair growth as a result of hair growth medications. Another big reason: stress, which can cause the amount of testosterone your body produces to fluctuate.