The most likely cause of this rash would be a local irritant reaction, or contact dermatitis, from an exposure to a new soap, personal care product, or other chemical. So it would be worth thinking about whether you have recently changed your routine or used a new product. Obviously, if so, eliminating the product would be an important part of treatment. You can also treat the rash by keeping the skin clean and dry (as moisture and sweating will irritate it), taking an over the counter antihistamine to relieve itch, and using an topical over the counter steroid cream to reduce the inflammation. If these do not work, you should see your doctor
to obtain a formal diagnosis and determine what needs to be done.
Other possibilities would include eczema
, which is an inflammatory condition of the skin characterized by redness, itching, and dryness. Similarly, fungal infections of the skin in the groin (jock itch) are common. The treatments for these conditions are all slightly different, so it would be best, if simple measures are not working, to talk with your primary care doctor
before experimenting with treatments in order to make sure that you are doing the right thing.