The histamine then causes the blood vessels to dilate and leak fluid, causing the skin to swell. This swelling irritates the nerve endings, which results in the itching sensation. A feeling of nausea, vomiting and dizziness may be present, in severe reactions. In a severe reaction the face and throat may swell causing problems with breathing, creating the danger of suffocation. Sometimes histamine is released by a nonallergic mechanism, but the hives are the same in appearance and symptoms.
Hives can appear on any part of the body, but are most common on the arms, legs and trunk.
The palms of the hand and the soles of the feet can also be affected. The common factors that are known to induce hives are food allergens, environmental factors, drugs, infections and infestations, synthetic products, emotional factors, systemic and general disease, physical factors and idiopathic causes. The common food allergens that can cause hives are seafood, berries, nuts, wheat, cereals, milk, cheese, eggs, peas, oranges, fish, chicken and chocolates. Fresh foods cause hives more often than cooked foods. The environmental factors that may produce an onset of hives are exposure to pollen, house-dust, animal dander, fungi, plants and extreme temperature changes.