Hello,
It can be due to chafing skin or dermatitis skin also apart from intertrigo of the skin. Wash the areas several times with fresh water. Do not use any cosmetic products at the sites. You can apply some calamine lotion at the rash as it will help in soothing the skin. Also wear cotton undergarments. Application of mild corticosteroid cream and oral antiinflammatories like ibuprofen/acetaminophen are also helpful. If the symptoms are severe then it will be best to consult a dermatologist.
I hope it helps. Take care and regards.
Try aloe vera. Be sure it is all natural -- no alcohol or chemicals. Vitamin E is often found in aloe vera gels but that is okay. It will calm inflammation, speed healing and reduce redness. If the area is still being irritated by constant friction, it might be a good idea to bandage the area after applying the gel to protect it. It may take a little getting used to, but this area of the body is quick to heal so you shouldn't have to put up with it for long.
All the best,
Brittany