Any ideas what this could be?

[Slashtrophe]

This appeared on 15 year old DS last week. It doesn't itch. Anyone have any ideas? All over chest and back

Looks very similar to a rash I had a few months ago, started with a few patches then spread all over my torso and upper arms. GP diagnosed it as pityriasis rosacea - prescribed my hydrocortisone cream and it was gone in a couple of weeks.

www.nhs.uk/conditions/pityriasis-rosea/

This mine at its worst

Thank you! I did a search in images and that sounds very likely. I’m glad yours cleared up

I second this. I had this when my daughter was 14 months old. I looked hideous, but it went away in some 6 weeks.
The "herald patch" on his chest is stereotypical.