Food Allergies Treatment

I have a 5 month old and he started to develop rashes under his eyes and neck ONLY. His usual formula changed its protein from somethin else to cow’s milk. so is this allergies from the milk? I live in a country with very hot and humid environment but its the rainy season now so i dont think its the heat. He also started consuming solids. I have given him carrots and papaya already (homemade) cud this be it?