Wheat is a kind of grass, but is his wheat allergy caused by ingestion of wheat or by being in a field of wheat? For example, I test positive for allergy to tomatoes, but I can eat them with no problem. Walking through a garden of tomato plants, however, gets me very itchy.
I used to get very itchy from sitting on the grass, especially if it had been freshly mown. The cut ends of the blades of grass would be leaking cell fluid in trace amounts, enough for a contact rash.
Was he, by any chance, rolling around in a heap of freshly mown lawn clippings? That'd do it, in almost anyone prone to allergies. All it takes is a speck in his eye and the tissues in that area get swollen and inflamed. I bet his conjunctiva is red, too. It sounds like a possibility that there is some contact allergy here, worse in the mucous membrane area; as distinct from an ingestion allergy, which is in his bloodstream via GI tract or inhalation.
Whatever it is - he has to learn to be careful in future and avoid skin contact with bare grass. If he wants to lie on the ground he should lie on a blanket. My mother swore by cheap cotton blankets - throw them in the washing machine, but they also shake clean really easily. Soft on the skin unlike wool, little chance of contact rash.
If he's prone to allergies like this be careful of natural remedies - many of them could expose him to further allergens. Basically, if it's good enough to be recommended as therapeutic, it's got active ingredients. if it's got active ingredients, however natural, they are still just as likely to cause allergic reactions as anything man-made. Possibly more so, because natural remedies often contain many other associated natural chemicals simply because they are a natural extract and not a highly refined synthetic. Try natural remedies by all means, just go as carefully as you would for anything else and take the same sort of notes. If something works without a problem - great! Make a note of it so you can go right back to the same thing next time. For example, I used to deal with a group, some of whom had allergies to salicylates, which are naturally occurring chemicals in many foods as well as herbs and spices. We had someone turn up to a meeting trying to sell his "natural remedy" as a "cure for everything, including allergies." He had no training apart from in sales and was trying to sell a therapeutic herbal product (by definition, almost guaranteed to be loaded with salicylates) to people who are allergic to them, as a cure for their allergy. It wasn't being sold as a homeopathic remedy either (plus there was no way he was a qualified homeopath).
You just have to be careful and apply the same standards.
I hope the hives settle down. nasty stuff. Have you taken photos for the doctor?
Marg
