Thanks for the question.
It is very uncommon to develop blackheads on the thighs. Some common causes of bumps on the thighs include keratosis pilaris, which is due to a clogging of the hair follicles.
There are also many different causes of dark spots or pigmentation of the thighs. This can arise commonly from post inflammatory hyperpigmentation from constant friction of the skin.
It would be good for you to see your doctor to get a proper diagnosis so that the appropriate treatment can be prescribed.
