What is hives?

Hives is also known as 'urticaria' or 'nettle rash'. This skin rash can have a range of triggers, most commonly an allergic reaction. Other triggers include medicines or infections. Sometimes the trigger is unknown.

What are the symptoms of hives?

The hives rash looks like raised bumps or welts on the skin that are usually itchy, but may also sting. These can be red or skin-coloured. The raised areas of skin are known as wheals.

Patches of hives often join together to form larger swollen patches or urticaria. The affected area of skin can vary in size from quite small to about as large as a dinner plate. The patches of hives often join together to look like larger swollen patches of urticaria.

The hives rash can last for a few minutes to hours, and usually disappears within 24 hours. In rare cases, the rash can last for weeks.

What causes hives?

A hives rash is caused when your body produces a substance called histamine. This is a protein released by the body in response to a perceived threat (trigger).

In most cases, it is not known what triggers this reaction. Sometimes, urticaria can occur in response to:

• an infection
• conditions that affect your immune system
• allergies to insect stings or bites, animals, plants or foods
• dye injected during a radiological test (for example, a CT scan)

Other triggers may include:

• cold air or water
• heat or sunlight
• vibration
• scratching
• sweating
• certain foods and drinks, such as spicy food, alcohol or coffee

In children, hives can be caused by a viral infection. This is why they sometimes go together with a cold or diarrhoea.

Hives that lasts for days at a time are almost never due to an allergy, apart from some cases of medicine allergy.

Stress rarely causes hives, but stress can make the symptoms worse.

When should I see my doctor?

You should see you doctor if you have a rash that looks like hives.

Some people have hives that don't go away or recur on a frequent basis. This is known as chronic urticaria. See your doctor if you have hives that keep coming back.

If you have taken antihistamines for your hives but they do not control the symptoms, discuss alternative treatment options with your doctor.

If your baby gets hives repeatedly, it's important to see your doctor. This could indicate an allergy to something they are frequently fed, such as cow's milk.

Sometimes hives can last for a long time. If you have hives for more than 6 weeks, your doctor may refer you for more tests to check if an underlying infection or chronic immune disorder is causing the symptoms.

How are hives diagnosed?

Hives is diagnosed clinically. Your doctor can diagnose the rash by talking to you and looking at your rash.

How are hives treated?

Hives usually resolve on its own without treatment. However, if the hives rash continues or gets worse, it can be treated with antihistamines. You can buy antihistamines over the counter at pharmacies.

Ask your pharmacist for advice on which antihistamine to take, as some will cause drowsiness, and can be taken at bed time if your rash is itchy and keeping you awake at night. Other antihistamines are not likely to cause drowsiness, so you can take them before driving or going to work or school.

To search medicines by active ingredient or brand name, use the healthdirect Medicines search feature.

Can hives be prevented?

If your hives are caused by a specific trigger, such as a food or medicine, you should avoid your known triggers.

Since most people don't know what caused their hives, it can be difficult to prevent.

Resources and support

For more information about the causes and management of hives see the Australasian Society of Clinical Immunology and Allergy website.

The Royal Children's Hospital has a fact sheet on hives for parents to learn about care at home and more severe reactions.

You can also call healthdirect on 1800 022 222 at any time to speak to a registered nurse (known as NURSE-ON-CALL in Victoria) for more information and advice.