Strange rash on 10 month old, any ideas?

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Hi all, first time parent here!

My 10 month old has this rash mostly around his trunk with some up his back and a few small marks on arms. I've been looking at baby rashes for the last hour and can't work it out. Looks most like heat rash but it's currently freezing and he's not overdressed. Anyone seen this before?

Thanks

Has he been poorly? Looks like a viral rash, or could be from irritation from clothes.

Looks like it’s kind of in the folds/nappy area. Is it pronounced around creases? If so I would guess sweat rash or irritation from clothes. If it’s all over then possibly viral. If well with no temperature I would just monitor for now.

Thank you for your reply. He's not quite himself, but not too out of sorts. I've certainly seen him a lot more upset with previous bugs that had no rash.

Thanks for the reply. At first I thought it was something to do with his nappy, and it is certainly more pronounced around that area, but on closer inspection it is running up his back and a bit on the arms. He's a little snotty but nothing too bad. I don't feel like he has gotten hot and sweaty, but perhaps he did and i hadn't noticed.

Hard to tell from pictures but my DD has had a similar rash a couple of times and I think it's a viral / post viral thing.

It looks the same as when my DS has had viral rashes, he's had them without been majorly ill before x

As others say looks like viral rash my dd had one similar lasted about 4 days.

Roseola?

Yes I'm leaning towards viral rash, even though he hasn't seemed that unwell at all. Will see how it looks this morning when he wakes up and report back.