Can taking biotin pills cause acne? or cause acne in those who already have the acne gene?

I suspect so: I could not find a study, but if anecdotal evidence is to be trusted on the basis of a great many self-reports -- unlike most other nutritional supplements -- i'll trust the popular experience of humankind. Especially if you're taking it just for your hair, it may be wise to stop. A few folks must take generous amounts of biotin for a genetic illness; if so, consider prescription rx for the acne.