Hives (acute and chronic urticaria)
What is hives?
Hives, also known as urticaria, welts, weals or nettle rash, is an itchy, raised rash on the skin, often accompanied by swelling.
Hives usually appear suddenly, sometimes because of an allergic reaction or being stung by a nettle. They form in response to histamine, which causes surrounding tissues to swell and become red. Histamine and other chemicals cause blood vessels to dilate and become leaky allowing fluid from the blood to leak out of the blood vessels causing itchiness and swelling.
How long do hives last?
They usually last for less than 24 hours, but in some cases they can last for several days or months before fading. Urticaria can be classified by its duration:
- Acute urticaria describes hives that clear up completely in less than 6 weeks. Around 1 in 5 people in the UK are affected by this over their lifetime.
- Chronic urticaria, which is rare, describes hives that last longer than 6 weeks and possibly last for years. This affects around 1 in 200 people in England.
What do hives look like?
The main symptom of urticaria is a red, raised skin rash. They can appear anywhere on the body, including the face, hands, lips, tongue, throat or ears. Hives vary in size (from a pencil rubber to a dinner plate), and may join together to form larger areas known as plaques.
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Symptoms of hives
Symptoms of urticaria include:
- Raised red rash
- Swelling of surrounding tissue
- Pain in the inflamed area
- Itching and burning of skin
What causes hives?
Histamine release and allergic reactions causing hives can be caused by many things including:
- Food ingredients
- Insect stings
If no cause is found it is known as idiopathic urticaria.
The most common causes of acute urticaria are:
- Latex (rubber)
- Insect bites
- Other health conditions
Some food that may cause hives when they are raw may not provoke a reaction after they are cooked.
Some food additives and preservatives in foods may also cause a reaction
Common foods causing acute allergic urticaria include:
- Fresh berries
Medications that can trigger acute urticaria include:
Chronic urticaria causes can be more difficult to identify. Some triggers are shared with acute urticaria, but additional causes can include:
- Autoimmune disorders
- Long-term infections
- Hormone conditions
Conditions linked to chronic urticaria include hepatitis, intestinal parasites and thyroid conditions.
Other possible triggers for some people include:
- Alcohol or caffeine
- Warm temperatures
- Pressure on skin
Types of urticaria
Doctors classify hives based on known triggers, including:
- Physical urticaria: Where the skin is affected by things like cold, heat, sun exposure, vibration, pressure, sweating and exercise. The hives may only be found where the skin was affected can appear within an hour of the exposure.
- Dermatographic urticaria: Hives caused after firm stroking or scratching of the skin.
- Solar urticaria: A rare form of hives caused by sun exposure.
- Cholinergic urticaria: Triggered by exercise, having baths, increased body temperature and stress.
- Urticaria pigmentosa: Mostly affecting children and causing distinctive brown or
red swellings or markings.
- Autoimmune urticaria: Hives linked to an autoimmune condition, such as lupus or rheumatoid arthritis.
- Urticaria vasculitis: Vasculitis where small blood vessels under the skin are inflamed.
- Idiopathic urticaria: No obvious cause found, but stress may be a trigger.