Or check the brand of softener u use to wash baby clothes. Certain brands, the softener smell stay on the clothes.
Don't think it is allergy. Have u fed baby antihistamines previously? If allergies, the rash should disappear
Check the baby detergent u are using. I heard before some brands may trigger reaction
If using fan at home. Buy the uniqlo AIRism mesh for baby. Helps a lot
Best to consult your pediatrician...
Could be heat rash related
Looks like heat rash