Thanks for your question on HCM. I can understand your situation and problem. In my opinion you should consult dermatologist and get done clinical examination to rule out infection. Skin infection is common if frequent rubbing is done. Another and more likely possibility is hormone induced changes in nipples and areola. Rubbing causes sexual excitement by producing oxytocin. This oxytocin is responsible for enlargement of nipples and areola during sexual excitement. It also causes dilatation of lactifarous glands and ducts and this can cause swelling under nipples. Oxytocin also enlarges montegomary glands. So all these can cause swelling under nipples while Rubbing. But better to rule out infection first.