Hello. Thank you for coming to JustAnswer with your question, and welcome.
This could be a contact dermatitis, or insect bites. But it seems if they were insect bites he would have other rashes on his body.
Either way, the skin is reacting to something, and it would be treated the same way.
So, he should keep his skin clean and dry. But do not use soap or hot water. Also, do not use hot compresses as this can aggravate the rash. He can use calamine lotion, or some hydrocortisone cream for the itching and rash. Cool compresses would be fine, and might be soothing. Benadryl is fine, also.
He should not use hydrocortisone on the rash for more than a week. He should see his doctor
---If the rash and itching does not improve within a weeks time,
---OR it gets worse, starts bleeding or becomes infected with increasing redness and warmth of the skin with drainage or swelling.