best way to deal with heat rash

[suzi2]

not strictly an allergy but...

DS (12wks) has bad heat rash under his neck & armpits. I don't think he's overly hot - just sweaty in the creases. He's also sick/drooling on his neck a lot. Although we clean him up straight away, I think he does it in his sleep too. It looks angry and a bit dry towards the edges.

What's the best way of tackling it? Leave it well alone to air?

Not really sure how to treat heat rash. What I thought was my 5 month old's heat rash turned out to be eczema due to food allergy. He was bf and proteins were coming through my milk. Sorry can't help - hopefully someone with more knowledge will come along soon.