What Are Hives?
Hives (urticaria) are red, itchy welts that can appear on any part of the skin and are usually caused by an allergic reaction. Hives can vary in size and may connect to form larger welts.
Hives usually go away on their own in less than a day, though new hives can develop as old ones fade, so hives can linger for several days. Acute hives are usually caused by allergies and last less than 6 weeks. Hives lasting longer than 6 weeks are considered chronic hives.
Large welts can also occur with hives, but deeper under the skin (angioedema). Angioedema often results in eyelid and lip swelling and is a medical emergency.
What Are Symptoms of Hives?
Hives may occur within minutes of exposure to a trigger or they can occur as a delayed reaction after more than two hours.
Signs and 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 at 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?
Hives are commonly caused by an allergic reaction. Common allergic triggers include:
- Foods
- Peanuts
- Tree nuts
- Shellfish
- Milk
- Eggs
- Fruits (especially citrus fruits and fresh berries)
- Wheat
- Chocolate
- Soy
- Pollen
- Insect bites and stings
- Parasites
- Some medications
- Animals
- Contact with something to which you are allergic, such as latex or nickel
- Allergy shots
- Scratching
Other common causes of hives include:
- Infections, including colds and infections caused by some bacteria or fungi
- Some illnesses
- Vasculitis
- Lupus
- Thyroid disease
- Exposure to sunlight (solar urticaria)
- Heat (cholinergic urticaria, also known as heat rash)
- Exposure to cold
- Water (aquagenic urticaria)
- Exercise
- Stress
- Pressure on the skin, such as from sitting too long, a tight waistband, or a heavy bag carried on the shoulder
- Contact with chemicals
- Scratching the skin
- Alcohol
- Vibration, such as clapping or mowing the lawn (vibratory urticaria)
How Are Hives Diagnosed?
Doctors can usually diagnose hives with a skin examination.
To diagnose the cause of the hives, tests may include:
- Allergy tests (on the skin or blood tests)
- Skin prick tests
- Enzyme-linked immunosorbent assay (ELISA)
- Radioallergosorbent test (RAST)
- Blood tests (to rule out an illness or infection)
- Complete blood count (CBC)
- Antinuclear antibody (ANA)
- C-reactive protein
- Sedimentation rate
- Thyroid stimulating hormone (TSH)
- A skin biopsy
What Is the Treatment for Hives?
For mild to moderate cases of hives antihistamines are usually recommended to relieve itching.
Chronic hives (lasting longer than six weeks) are also treated with prescription antihistamines.
Medications used to treat hives include:
- Antihistamines
- Loratadine (Claritin)
- Fexofenadine (Allegra)
- Cetirizine (Zyrtec)
- Desloratadine (Clarinex)
- Diphenhydramine (Benadryl)
- Hydroxyzine pamoate (Vistaril)
- Doxepin (Zonalon)
- Corticosteroids (short-term use)
- Dapsone
- An antibiotic that also relieves redness and swelling
- Monoclonal antibodies
- Omalizumab (Xolair) for difficult-to-treat chronic hives called chronic idiopathic urticaria (CIU)
- Histamine (H-2) blockers
- Antidepressants
- Doxepin (Zonalon) in cream form can help relieve itching
- Asthma medications with antihistamines
- Immune-suppressing drugs
- Cyclosporine (Gengraf, Neoral, others)
- Tacrolimus (Astagraft XL, Prograf, Protopic)
Severe cases of hives or angioedema may require an injection of epinephrine (EpiPen or shot of adrenaline).
