Skin Condition

Ok. So, Harrison has a skin condition. He's had it once before and I decided at the time that it was 'heat rash' because it was on his back, neck, armpits and we had been traveling a lot with him in the hot car seat. But now I'm thinking it's not 'heat rash'. Perhaps, eczema and/or a possible food reaction? It doesn't seem to bother him. It seems to be getting better. I'm applying lotion daily. It's dry, red, and raised and only on his back this time. What do you think?