Hives appear on the skin as red, raises, itchy rashes that are sometimes triggered by allergens. When the body is faced with an allergic reaction, the body releases a protein called histamine. When histamine is released, our capillaries leak fluid; the leaked fluid is what accumulates in the skin and promotes the rash. Hives, are also commonly referred to as uticaria, welts, or nettle rash. Uticaria can be triggered by: