It might actually end up being hormonal, especially if they occur more often during a particular part of your cycle. Sorry I can't be more help.

http://www.pregnancy-info.net/forums/signs_of_pregnancy/pimples_on_nipples_not_areola_/

When you pregnant you can get white pimple like things on your nipples, but hormones before your period can also make them look this way.

acne on nipples? cmon

acne on nipples? cmon

Acne can happen anywhere on the body . I had one on my penis when I was in my 20's and kept on reoccurring