My son also has red bumps and sort of blisters- started on his arms and moved to his legs.  I think it is a reaction to roundup weed killer.  Any chance anyone else thinks this.  We live in a city where there is no grass and he never gets this.  He used to have this reaction every time we went to a house outside the city- everyone told me it was poison ivy except we never found poison ivy in the yard.  I kept telling the gardner to make sure they kill anything that might be poison ivy or oak or sumac.  They would use weed killer and we would never find the poison ivy.  we stopped going to the house and he stopped getting the reactions.  Now 3 years later we are visiting another house every month or so with tons of grass, weeds and he has no problems.  3 days ago they sprayed round up everywhere to get rid of all the weeds and the next day he got red bumps with a bit of white in them on his arms then his legs and his eyes got red.  Maybe someone can find the same connection.  I can't find any link between the weed killer and a skin reaction in print but maybe someone else can.