Sunhat causes nasty sweat rash

[Missmiller]

Hi all

My 3 year old always gets a very itchy, nasty rash in his hair and on his forehead when he wears a sunhat. He also gets this in winter if he wears a warm hat. This has been the case since he was a baby. The rash always looks very angry and irritates him so much. Has anyone else experienced this and if so, what solutions have you found please?

Forgot to write...The rash always lasts at least a week after it starts