Toddler skin rash question?

My son is 21 months old. he has had a red bumpy rash on the back of his neck for a couple days. (It's not pimply or anything.) At first, it just looked like he got a little too hot and had irritated skin where his shirt rubbed. Now it's worse and spreading a little down his chest. It doesn't itch because he is ignoring it and when I touch it it doesn't bother him! Does anyone have any ideas? thanks!|||Try using hrdocortisone. I use that on my son, He gets the same thing. He get prickly heat when hes in the heat for too long, and I believe he has a mild case of egzema. There is a prescription that clears all skin rashed but mainly but they dont like to us it in children under 2-3 do not remember. Dress him in pure cotton clothing .. Try washing his clothes only in hypoallergenic detergent like dreft or all free and clear .. Give him baths with soaps that dont have perfumes etc. The best one for my son was Cetaphil and they also carry the lotion. for itchy irritated skin. And then on top of the lotion put the hydrocortison. I hope this helps and it clears up soon. Good Luck|||maybe its a heat rash, but i would call the doc