Hives in adults may be caused by coming in contact with something that is an irritant to your skin or you are allergic to, or maybe eating something you are allergic to. If you started some medications you may be having a reaction to the medicine. If you are not having any shortness of breath try taking some Benedryl. If the hives do not resolve themselves you should see your physician. If you having shortness of breath you need to be seen by a doctor right away.