Strange itchy rash on DS's head - any ideas?

[Jen1978]

Hi
dS1 is 14 months and has been scratching his head a lot over the last few days. Nothing obviousl to see, but today on closer insepction there is a rash on the back of his head, around his hair line which gets redder when he scratches it.
His hair is very long (desparately needs cutting) and he gets really sweaty head and damp hair when he has a nap during the day despite putting him in only a 0.5 tog grobag and short sleeved vest (his room isn't even that warm, 23 C max). Could it be sweat rash? What can we do to ease the itching. Obviosuly going to keep him cool, and going to get his hair cut asap. Is there anything we can wash into his hair to help. Any ideas on what else it could be, or does it sound like sweat rash? Think he gets very hot in the sleep room at nursery (goes 5 times a week) despite the thin grobag. He has always had quite a sweaty head even since he was tiny!