did he play with any foam floating toys???
what was the allergic reaction like? a rash or actual hives?
My kids broke out every time they went to the pool but pretty sure it was the foam float pads and tubes they had there for them to play with.
you can certainly have your child tested for allergies..
also I don't know if there is any latex in those floatie things either.. but that is a common allergy..
and there is also a thing called oral allergy syndrome - if your son has been tested positive for any of a number of plants/trees/weeds he may have reactions to other substances. You can google "oral allergy syndrome" or "allergic cross reaction" to learn more about it.
Many kids with eczema also have allergies. At least two of my kids who have had severe eczema have tested positive for numerous allergies.. including food and plant pollens.