As you can see in the attached photo, for some years now, whenever I exert myself physically (especially if to the point of sweating) or taking a hot shower (which I avoid, but still), my forehead and temples (and sometimes around my eyes) break out in a blotchy red
rash. Though my face may feel a bit warm, there is no other itching or physical sensation involved.
It appears to be body temperature/heat related as water alone (from a shower, sweat, etc.