Posted in Children's Health but no responses, so thought I'd try in here instead 
. Posted this yesterday, so now more than 24 hours since it happened, and his eye is still red, although no other ill effects.
"DS3 is 5 months, no history of allergies etc. Today DH and I took him up to school to see a concert DS1 was in, and put him in the Phil&Teds (mention this only in case anyone is aware that they use a particularly unusual ingredient in their raincovers...) with the raincover on.
Being a nosey sort of baby, and starting to be at the shove-everything-in-the-mouth phase, he was grabbing at the raincover and pulling it towards him to chomp on it. It ended up being over his face on the left side. Went into the concert, plucked DS3 out of the pram - and realised his face on the left side was all red and blotchy, his eye was swollen and weeping a lot, so that he looked as if he were crying. After a couple of hours it went down.
Not really worried, as it wasn't a severe reaction and he has been fine since. Just curious, really, wondered if anyone else has experienced this, and what in the raincover could have caused it - latex? Can't think what else could have caused it, so fairly sure it was the raincover. Most odd..."