Allergy or heat rash?

Stephanie • Married 2 years, 4 baby losses. Jun 2017, chemical. Dec 2017, missed miscarriage. Jul 2018, ectopic, lost left tube. Nov 2018, missed miscarriage.

We started introducing PB this week and I noticed he started getting this on his neck and a little on his body. It doesn’t turn red after he eats it. We’ve done PB 3 days now. I fed him the PB around 1 PM and it’s now 7:30 PM and I didn’t see it after I fed him.

It’s also been quite hot the last few days, so I’m not sure if it’s a heat rash or allergy. Any thoughts?