The itching may be due to tight clothes or your nipple rubbing against your bra or under shirt. This can happen if you exercise without a bra. However, chronic itching can also be a sign of eczema.
If the itching is bothersome, obtain hydrocortisone cream over the counter and apply it 3-4 times day. If this problem persists after application of hydrocortisone, it is wise to see your doctor. Another common cause of itching around the nipples is a fungal infection, which can also be easily treated with an anti fungal cream.
If the itch is limited only to your nipples, perhaps a change of fabric or bra may be warranted