Evelyn:
They are a kind of cyst, which many women (and men) have around their nipples. The "white
substanceDrug abuse" is regular cust contents -- dead skin cells, etc. -- rather than pus. There's no need to do anything about these cysts, though light electrocautery can minimize them if they embarrass you. The're not related to keratosis pilaris, which consists of bumps of keratin protein on the outer arms.
Best. Dr. R
Show 'em to your doc next visit, just to be sure.
Dr. R