Rash on child's forehead

[Dave999]

My nine year old son has been developing a rash on his forehead every summer for the past three years. It is only on his forehead and nowhere else on his head or body. It only comes on in the summer. He has no other health issues.
It varies in severity through the day and in the space of an hour can go from being very visible to hardly noticeable.
I suspect it is heat related.
A pharmacist has suggested anti hystamine cream, however this has had little effect.
See attached photos
Any suggestions!

It just looks like spots? If it's in the summer, more sweat, more sebum? Is it itchy? Sore?

It is spots, but I am not sure why they come along every summer and are just confined to his forehead.
They are not itchy or sore.

Hi there Dave999 - I can see this was last year but my 6 year old daughter seems to have the same rash. We have tried anti-histamine. Did you manage to work out what it was?