Chin hair can be unwanted by many women.
If you have no detectable cause for the chin hair it is called idiopathic hirsutism.
Abnormal hormone levels, abnormal menstural cycles and other signs of PCOS can be the cause of dark, coarse, unwanted chin hair or hirsutism that has a cause.
Elevated male androgen blood levels in women can have the side effect of causing these thick dark chin hairs.
Other causes of steriod hormone imbalances can lead to chin hair growth as well.
Changing chin hair growth, whether bothersome or not, should be evaluated by your gyno.