What Are Hives (Urticaria)?
Hives usually go away on their own in less than a day, but new hives can develop as old ones disappear, so hives may linger for a few days. Acute hives are usually caused by allergies and last less than 6 weeks. Chronic hives last longer than 6 weeks.
Large welts can also occur with hives, but deeper under the skin (angioedema). Angioedema can result in eyelid and lip swelling, and is a medical emergency.
What Are Symptoms of Hives (Urticaria)?
Hives (urticaria) may occur within minutes of exposure to a trigger or they be a delayed reaction that happens after more than two hours.
Symptoms of hives include:
- Slightly raised, pink, or red welts (wheals)
- Welts may vary in size from as tiny as a pen tip to as large as a dinner plate
- Welts may occur alone or in a group, or connect over a larger area
- Itching (may be severe)
- Skin swelling
- Usually subsides within 24 hours in one spot but may appear in another spot
- May be accompanied by angioedema, which is swelling deeper under the skin that can cause eyelid and lip swelling
- Angioedema is a medical emergency; see a doctor if this occurs
What Causes Hives (Urticaria)?
Hives (urticaria) are commonly caused by an allergic reaction. Common allergic triggers include:
- Tree nuts
- Fruits (such as citrus fruits and fresh berries)
- Insect bites and stings
- Allergy shots
- Some medications
- Contact with something to which you are allergic, such as latex or nickel
Other common causes of hives include:
- Infections, including colds and infections caused by some bacteria, viruses, or fungi
- Exposure to sunlight (solar urticaria)
- Exposure to heat (cholinergic urticaria, also known as heat rash)
- Exposure to cold
- Water (aquagenic urticaria)
- Certain illnesses
- Pressure on the skin, such as from a tight waistband, sitting too long, or a heavy bag carried on the shoulder
- Contact with chemicals
- Scratching the skin
- Vibration, such as clapping or mowing the lawn (vibratory urticaria)
Are Hives (Urticaria) Contagious?
Hives (urticaria) are a symptom and in themselves are not contagious, and most causes of hives are not contagious. Hives are typically due to an allergic reaction or other non-contagious trigger.
If hives are caused by an infection such as from bacteria, viruses, or fungi, the cause of the hives may be contagious and may be spread through respiratory droplets when an infected person coughs or sneezes, or by direct skin-to-skin contact, depending on the germ.
How Are Hives Diagnosed (Urticaria)?
Hives (urticaria) are typically diagnosed with a skin examination.
Tests used to diagnose the cause of hives may include:
- Allergy tests (skin or blood tests)
- Skin prick tests
- Enzyme-linked immunosorbent assay (ELISA)
- Radioallergosorbent test (RAST)
- Blood tests (to rule out illness or infection)
- Skin biopsy
What Is the Treatment for Hives (Urticaria)?
Mild to moderate cases of hives (urticaria) are usually treated with antihistamines to relieve itching.
Chronic hives that last longer than six weeks are also treated with prescription antihistamines.
Medications used to treat hives include:
- Corticosteroids: for short-term use only
- Dapsone: an antibiotic that also relieves redness and swelling
- Monoclonal antibodies: omalizumab (Xolair) is used for difficult-to-treat chronic hives called chronic idiopathic urticaria (CIU)
- Histamine (H-2) blockers
- Antidepressants: doxepin cream (Zonalon) can help relieve itching
- Asthma medications with antihistamines
- Immune-suppressing drugs
Severe cases of hives or angioedema may require an injection of epinephrine (EpiPen or shot of adrenaline).