Localized hives to left lower arm, from elbow to wrist. appears as red circles, randomly dispersed. appeared 3 days ago. left elbow randomly started to itch on and off, hives appeared rapidly. only mild itch now. dime sized?

The cause of hives can be quite elusive. If they only appear on one arm, I'd have to think that the cause would be more of a physical trigger like contact with a certain substance or from pressure on that arm while your skin is in a state of heightened reactivity. An allergist is best to advise you.

Your arm may have been exposed to something you are reacting to, called a contact dermatitis. You could try an over the counter hydrocortisone cream to treat it. If it doesn’t go away, see a doctor to diagnose and treat it after examining it. Good luck to you!