Is this heat rash or eczema?

Crystal

My son does have eczema but it’s never been this bad but it’s been really hot in our town. We were at a park yesterday and he did get a little sun burnt, but I didn’t know if this was heat rash or if it’s just his eczema. It’s on his face, neck, chest, arms, back and a little on legs. We plan on making an appointment this week with the pediatrician regardless.