Hives (Urticaria)

• Raised, red or white welts (wheals, or swellings) of various sizes
• A single welt or group of welts that can cover large areas of skin
• Welts that resolve while new welts erupt, making it seem as if the condition "moves"
• Burning or stinging in the affected area
• Itching, which may be severe

Hives can be either acute or chronic. By definition, acute hives can last from less than a day to up to six weeks, whereas chronic hives last more than six weeks — sometimes occurring for months to years at a time.

Angioedema

Angioedema is similar to hives but occurs deeper in the skin. Signs and symptoms of angioedema include:

• Large, thick, firm welts
• Swelling of the skin
• Blisters (bullae) in areas of severe swelling
• Pain or warmth in the affected areas
• Difficult breathing or swallowing, in severe cases

Angioedema often appears near your eyes or lips, but can also develop on your hands, feet, genitalia or inside your throat. Angioedema and hives can occur separately or at the same time.

Hereditary angioedema is a more serious — yet uncommon — condition that can cause sudden, severe and rapid swelling of your face, arms, legs, hands, feet, genitalia, digestive tract and airway. Signs and symptoms of hereditary angioedema include:

• Sudden and severe swelling of the face, arms, legs, hands, feet, genitalia, digestive tract and airway
• Abdominal cramping as a result of digestive tract swelling
• Difficulty or obstructed breathing due to swelling of the airway

Causes

Hives and angioedema are caused by inflammation in the skin. In some cases, hives and angioedema are triggered when certain cells (mast cells) release histamine and other chemicals into your bloodstream and skin.

Allergic reactions to medications or foods can cause acute hives or angioedema. Many allergens have been identified. Examples include:

• Foods. Many foods can cause problems in sensitive people, but shellfish, fish, nuts, eggs, chocolate and milk are frequent offenders. Food additives, such as salicylates and sulfites, are other potential allergens.
• Medications. Almost any medication may cause hives or angioedema; common culprits include penicillin, aspirin, ibuprofen and blood pressure medications.
• Other allergens. Other substances that can cause hives and angioedema include direct contact with pollen, animal dander, latex and insect stings.

Additional triggers that may produce hives or angioedema include:

• Physical factors. Environmental factors can result in the release of histamine with subsequent hives or angioedema in some people. Examples of these factors include heat, cold, sunlight, water, pressure on the skin, emotional stress and exercise.
• Dermatographia. The name of this condition literally means "write on the skin." When pressure is applied to the skin or the skin is scratched, raised lines appear on those areas due to histamine-based angioedema that leads to swelling beneath the skin.

In addition to these triggers, hives and angioedema sometimes occur in response to your body's production of antibodies. This may occur because of blood transfusions; immune system disorders, such as lupus or cancer; certain thyroid disorders; infections, such as hepatitis; or even a cold.

Hereditary angioedema is an inherited form of angioedema and is related to low levels or abnormal functioning of certain blood proteins (C1 inhibitors). These inhibitors play a role in regulating how your immune system functions.

Risk factors

You may be at greater risk of hives and angioedema if you:

• Have had hives or angioedema before
• Have had other allergic reactions
• Have a disorder associated with hives and angioedema, such as lupus, lymphoma or thyroid disease
• Have a family history of hives, angioedema or hereditary angioedema

Complications

Hives and angioedema can cause:

• Itching
• Discomfort

In more serious cases — such as when swelling occurs inside your mouth or throat — complications can include:

• Difficulty breathing
• Loss of consciousness
• Anaphylactic shock

Anaphylactic shock (anaphylaxis) is a serious allergic reaction involving your heart or lungs. Your bronchial tubes narrow, it's difficult to breathe, and your blood pressure drops, causing dizziness and perhaps loss of consciousness or even death. Anaphylactic shock occurs rapidly, and requires immediate medical care.

Diagnosis

Your doctor will begin by asking you about your medical history. This may include asking you to create a detailed diary of exposure to possible irritants. It's important to tell your doctor about all medications you take, including over-the-counter (nonprescription) drugs and herbal remedies, even if you don't take them every day.

If the cause of your hives or angioedema isn't apparent or if your symptoms recur often, your doctor may recommend an allergy skin test.

• Puncture, prick or scratch test (percutaneous). In this test, which is the type of skin test most commonly performed, tiny drops of purified allergen extracts are pricked or scratched into your skin's surface. This test is usually performed to identify allergies to pollen, animal dander, foods, insect venom and penicillin.
• Intradermal test (intracutaneous). Purified allergen extracts are injected into the skin of your arm. This test is usually performed if your doctor suspects that you're allergic to insect venom or penicillin.
• Patch test (epicutaneous). An allergen is applied to a patch, which is then placed on your skin. This test can identify substances that cause a reaction when coming in contact with your skin. Tested substances may include latex or medications.

If your doctor suspects hereditary angioedema, he or she may ask for blood tests to check for levels and function of specific blood proteins.

References:

http://www.medicinenet.com/hives/article.htm

http://www.healthline.com/health/angioedema

http://www.emedicinehealth.com/hives_and_angioedema/article_em.htm

http://www.msdmanuals.com/home/immune-disorders/allergic-reactions-and-other-hypersensitivity-disorders/angioedema

http://my.clevelandclinic.org/health/diseases_conditions/hic_Urticaria_Hives_and_Angioedema