Usually a anti-histamine medicine as in Piriton, but there are various causes of hives, wikipedia has a page on it http://en.wikipedia.org/wiki/Urticaria

Several Run cold water over them until they ease up. This can take a while. The colder the better. Place a washcloth with ice between you and the faucet if you can. Wash the area vigorously with a soapy wash cloth for two minutes then apply a paste made with baking soda and water. (toss the cloth in the laundry bin - do not use it again before it is laundered) If neither of these work AND YOU KNOW you can safely take Benedryl then - Benedryl - Liquid to take inside and creme for the outside. Good luck

Mother Earth pretty much covered it but here is one that can help with the itch: If you can get collodial oatmeal (Aveeno makes it) run a bath, put in the collodial oatmeal as directed, soak, then, when the hives are finished, clean out the messy tub. Aveeno makes soap now. Caladryl was an old OTC topical ointment that helped. If you want to get old school, Calamine. I think that they are still available. Big thing is if you scratch, the problem gets worse. If you have a recurring problem with hives, you are allergic to something and should see your doctor. Once you find the triggers, you can avoid them or take medicine to control your reaction to them. Benadryl always works well for me but, as Mother Earth said, only take it if you already know that you are fine with it.

Hives are usually the indication of an allergic reaction, although the exact cause is often difficult to pinpoint. The irritation can be caused by a number of circumstances, including environmental factors, like pet dander, dust mites, pollen, or mold. Other causes could range from insect bites to stress. Hives develop primarily as the result of certain cells in your body releasing histamine. This secretion of histamine traps fluid under your skin and this buildup causes the outbreak of Hives. Hives can last for a few minutes or hours and then disappear or last for weeks or months at a time. Since hives are caused by the chemical histamine, it makes sense that you would treat them with an antihistamine medication, such as diphenhydramine (Benadryl). Other sedating antihistamines that are sometimes used to treat hives include hydroxyzine (Atarax) and cyproheptadine (Periactin). Non-sedating antihistamines, including Allegra, Claritin, Clarinex, and Zyrtec, are also used to treat hives, expecially hives that last longer than 6 weeks. You should also avoid hot baths or showers and avoid irritating the area with tight-fitting clothing. You can use topical medication such as calamine lotion to help dry the hives and calm the itch. Less commonly, a you may need a steroid to treat your episode of hives. Other treatments can sometimes include doxepin (Sinequan), an antidepressant that can work as a potent antihistamine, montelukast (Singulair), and medications such as ranitidine (Zantac) or cimetidine (Tagamet), which are more commonly used to treat reflux. If you have a severe reaction don't wait to get to an ER or call 911. Call 911 if you experience:Tightness in your throat, Shortness of breath, Tongue or face swelling, Fainting, or Wheezing. This could be very serious! If hives become a common problem for you, you should consult with a health care professional for advice. Good luck to you. http://www.medicinenet.com/hives/article.htm http://www.webmd.com/allergies/guide/hives-urticaria-angioedema http://www.nlm.nih.gov/medlineplus/hives.html