Urticaria (also called hives) is a histamine response, and antihistamines should calm it - antihistamine cream on the area, or oral antihistamine if it is severe. Avoiding the cause is the usual long-term treatment. Some people react this way to cats, pollen or fruit. Some people claim that a cool bath containing bicarbonate of soda will sooth the itching, but that never worked for me.
Sometimes urticaria can be caused by, or made worse by, another factor like impaired liver function or sinusitis, in which case it might subside if that factor is treated.