Did it occur after he was lying outside in grass? If so, it is probably a kind of gnat or small flying insect bite. The bites can occur in high numbers and look like a skin infection. The "rash" caused by these gnats is quite distinctive, and if you could post a photo it would be easier to diagnose. A single bite looks like a red ring with a slightly raised center. This particular rash has been very common this spring. Cortisone cream can be applied to the rash if your dog will not lick off the cream, (most dog's will lick it off). Oral Benadryl may help. The dose for Benadryl is 1mg per pound up to 3 times per day. If these measures are ineffective, please take your dog to the vet for evaluation and treatment.
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