Hives or what else is it?

Last Sunday Cobalt broke out in hives. In the past when he's done this it was caused by bugs since the barn they were at was really swampy. So Monday, Wednesday I gave him a Viodine bath and Tuesday I hosed him off with cold water and I made sure to keep him fly sprayed. Thursday it was getting worse so the vet gave me an antihistimine to give him which I did Friday morning (vet never saw him, just prescibed the shot from my description). Sunday it still hadn't gone away, so I tried feeding him a different hay last night to see if the hay could have caused it (I got a new load in 2 weeks before this started). I got to the barn this morning and it was WORSE :( ! Before he only had it on his chest and neck but now it's all over. In his armpits, belly, by his stifle and any place on him that could accumulate sweat. I called the vet back immediately this morning, but he's getting ready to get into surgery. I don't think this is life threatening since he's eating, drinking and pooping so he's going to call me back as soon as he gets out and let me knwo when he can head over.

Any ideas on what else to do? The only thing I can really think of is cool baths. Anyone know what else it could be? The antihistimine I thought would take care of it!

Could be a lot of things. Some horses react more to the treatments than if just left alone. Fly sprays can cause bad reactions, too. Is it a light colored horse? They seem more prone to react to irritants, from bugs to chemicals to sunshine.

Fly sprays can cause bad reactions, too.
Is it a light colored horse? They seem more prone to react to irritants, from bugs to chemicals to sunshine.

He actually got the reaction when I wasn't using fly spray on him. It's also the same fly spray I've been using on him for 2 years. He is a bay with an extrememly small amount of white on him.

Shiloh has an allergy or something too. She gets it in the same place as your. We give her antihistamines and bathe her with alodine shampoo. We found bag balm worked best as a salve.
I honestly don't have a clue what causes it, bugs, plants or just sensitive skin. My first thought was that she had gotten into a fire ant hill, but it was her underside that was the worst.
Don't freak out too badly unless you notice any swelling around her nose which could restrict her breathing.
The vet can give her a shot of epinephrine (sp?) or something like it if need be. You should still have your vet out just to be on the safe side. We have though of having her tested to narrow down the possibliltys but the cost has held us back. For now we just treat the itchys and go on.

Something similiar happened to a mare of mine last year. She looked like from her throat to her tail and down to her knees/hocks, she had misquitoe bites everywhere! I fought with this for 3 weeks, had the vet out, used cortisone cream on her entire body, used benadryl in her feed, everything I could think of. Finally I started to remove supplements from her feed so all she was eating was grain, then I added them back in slowly from the order of what I had been using the longest on her. When I got to the last thing (which was black oil sunflower seeds) she broke out again! This was my problem and this is how I found out she was highly allergic to them. Not saying it could be just about any kind of an allergic reaction, but maybe she is eating something new, either a supplement or maybe something she found outside or something someone else might be giving to her...

I also thought the antihistamine would take care of mine, but soon found out that if the allergen is still getting to the horse, then this is not true!

Had the vet out this afternoon. He gave Cobalt a shot and then I have to give him some antihistimine medicine in his feed 2x a day. If it's not gone by Monday we are going to start eliminating things from enviorment and food.