What can cause sudden very red very itchy dry patches over nipples. no change in toiletry products, washing powder etc. not pregnant. no new medications. thanks?

It may happen at times without an apparent reason, atopic dermatitis is one of the reasons. The condition is most often benign. You can apply lidocaine cream or ointment 4% (OTC) on the nipples (for relieving the itch), several times a day until the sites normalize. Do not scratch or pick the sites. See your doctor if the condition does not improve after this week.