I have no idea what is causing these. Poor Rupert has these horrible hives. I came home from work on Wednesday, took him out of his crate (he is in there for about 4 hours in the afternoon) and that's when I first noticed them. It is a wire crate with a plastic tray in the bottom. It has a metal water dish, a bed and a blanket inside. It is the same setup he's had for a long time.
I called the vet right away and he said to give him 3 benadryl tablets every six hours for two days. I took the blanket and bed out of his crate, pulled out the tray, and searched all over for spiders, bees, bugs, etc. but didn't find anything. He had been stung once about a year ago by a hornet and it puffed up a little, but just in that one spot. Nothing like this.
recently buy Bounce fabric sheets, that's the only thing I can think of that's new. I just washed the sheets on our bed (Rupert sleeps with us at night) and I washed Rupert's blanket that goes in his crate - both about a week ago - but I do not use fabric softener sheets on either of those. I'm pretty sure there could be residue left behind in the dryer from previous loads, though. Either way, I don't think I'll continue using that brand anymore.
I continued the benadryl, but the hives kept coming back. This morning it was so bad. His legs were covered. I had to bring him in for an injection. Now he's on a steroid pill. Prednisone, 20 mg once a day for three days, then 10 mg (a half pill) for two days.
After I post the pics I'm going to do some searching, I think I remember seeing something about milk thistle, or some holistic things to give when your dog is on steroids. Callie? Jennie?
Anyway, here are some pics I took when I first noticed it. It got worse than this, but I ran out of film.