What would you say this rash is? Allergy?

[Tittie]

DS gets this rash which comes and goes occasionally. It's never there for long so we never get to a doctor in time! I thought it looked like an allergy but I have no medical background. What do you think?

I've never seen that before. I wonder what it could be? I'd show this photo to a pharmacist if it was me.

That looks allergic, like mild urticaria

Try giving an antihistamine and see if it goes down? Or cream.