14yo covered in "heat rash"

[FurtherSupport]

This boy never gets ill (touch wood!) and doesn't seem unwell now but is covered in a small pin prick rash. Any need to be concerned?

Does it blanch with the glass test? Are you sure it's a heat rash?

No I'm not sure it's a heat rash, I always understood there's no such thing but it's the kind of rash that's often described as heat rash.