Hives is an outbreak of swollen, pale red bumps or plaques (wheals) on the skin that appear suddenly, typically as a result of the body's reaction to an allergen. Hives usually itch and may also burn or sting. They can appear anywhere on the body, in a range of sizes from a pencil eraser to a dinner plate – they may join together to form a larger area known as a plaque. An outbreak can last up to 24 hours before fading.
Hives form in response to histamine – a chemical released by cells in response to injury and in allergic and inflammatory reactions. Allergic reactions, certain foods, insect stings, sun exposure or medications can all cause histamine release making it difficult to identify the exact trigger.
Your dermatologist can help you identify the triggers for your hives. Skin tests may be performed to determine the trigger and routine blood tests can be done to determine if there is a larger illness present. There are several types of hives:
Acute urticaria presents as hives lasting less than six weeks and is most commonly caused by foods or medications – some common offenders include:
Foods: nuts, chocolate, fish, tomatoes, eggs, fresh berries, and milk. Fresh foods cause hives more often than cooked foods.
Medications: aspirin and other nonsteroidal anti-inflammatory medications like ibuprofen, high blood pressure drugs (ACE inhibitors) and painkillers like codeine.
Chronic urticaria is defined as hives lasting more than six weeks. The trigger for chronic urticaria is often more difficult to identify, and in some cases the cause may be thyroid disease, hepatitis, infection, or cancer. Over time these hives can affect other internal organs such as the lungs, muscles, and gastrointestinal tract. Symptoms include muscle soreness, shortness of breath, vomiting, and diarrhea.
Physical urticaria are hives caused by direct physical stimulation to the skin by cold, heat, sun, pressure, and sweating. The hives usually occur at the site where the skin was stimulated and rarely appear elsewhere. Most of the hives appear within one hour of exposure. Dermatographism is a common form of physical urticaria where hives form after firmly stroking or scratching the skin.
Antihistamines are usually prescribed by your doctor to provide symptomatic relief. If antihistamines don't provide relief, other treatments will be considered, including a newer medication, omalizumab (Xolair), which is approved to treat chronic hives in patients over 12 years old. For severe hives or angioedema, an injection of epinephrine (adrenaline) or cortisone may be needed.
If hives occur with dizziness, wheezing, difficulty breathing, tightening of the chest, swelling of the tongue/lips/face, immediate medical attention should be sought immediately.