How to treat rising under my breast.

You mean rash?: If you are talking about a rash - then you can try any over the counter antifungal products to help you. A rash under the breast is often caused by Candida, because it can be moist and sweaty there - which the germs love! It's food for them. So if you can elevate, keep the area dry and apply an antifungal (powder would be ideal -even a 'foot powder for fungus') that should make it go away.