Hello,
It can be due to contact dermatitis, allergies, eczema or scabies. He should 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. He can take some OTC oral antihistamine medications like Benadryl or Claritin and see if it helps.
For mild-moderate symptoms a weak steroid may be used (e.g. hydrocortisone as dermacort), whilst more severe cases require a higher-potency steroid (e.g. clobetasol propionate, fluocinonide).But they are available under prescription and should be taken only after consulting a dermatologist.
If the symptoms persist then scabies should be ruled out.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
He may not realize he might have eczema. This is a lifelong condition and the only real practical way to deal with eczema is through diet. Look up things like "foods not to eat with eczema" and "diet for eczema". The general consensus is that gluten and dairy should be avoided. I wish conventional doctors would tell their patients this, because not eating gluten and dairy is the only long term solution that helps me. Make sure you do the research, though. There is more to it, but conventional doctors fail to tell their patients about diet, so they're doing their patients a disservice.