Mystery appearing/disappearing rash in 4yo - plus stinging lips?!

[Jacksterbear]

4yo DS has been complaining of stinging lips for the last 3/4 days. And on Friday night and Sunday night (but oddly not Sat night) he has come out in a rash on his back, chest and arms (like nettle rash) at about 10.00 p.m., woken screaming and scratching himself to pieces, been given antihistamine, settled after an hour or so, and the rash has disappeared by morning. WHAT on earth is that about? Can't think of anything on the allergies front e.g. no different/new food eaten, no new washing powder etc. Any ideas? TIA!

Could the rash have been from sweating, eg heat rash? Not sure about the stinging lips though, that sounds more like some form of allergy. I would make an appointment with the GP given how serious allergies can be/become.

Thanks for the reply. Yes I suppose heat rash is possible - has assumed it was connected with the lips things though (which is not necessarily the case) and that therefore the whole thing was likely to be allergy-related. Hmm how odd.