My son has a blotchy red rash only on his arms and a little on his thighs. It's not bumpy but smooth. He also said it's itchy. I thought it might be an allergic reaction and I gave him some allergy medication, but it doesn't seem to be subsiding. What could it be and how can I get rid of it.

My son has a blotchy red rash only on his arms and a little on his thighs. It's not bumpy but smooth. He also said it's itchy. I thought it might be an allergic reaction and I gave him some allergy medication, but it doesn't seem to be subsiding. What could it be and how can I get rid of it.
Sounds like urticaria, or an allergic reaction, but it's impossible to tell without seeing it. If Benadryl doesn't make it go away, go see your doctor.