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Nettle rash Content Supplied by NHS Choices
Introduction

Urticaria - also known as hives, weals, welts or nettle rash - is a raised, itchy rash that appears on the skin. It may appear on one part of the body or be spread across large areas.

The rash is usually very itchy and ranges in size from a few millimetres to the size of a hand.

Although the affected area may change in appearance within 24 hours, the rash usually settles within a few days.

Doctors may refer to urticaria as either:

  • acute urticaria - if the rash clears completely within six weeks
  • chronic urticaria - in rarer cases, where the rash persists or comes and goes for more than six weeks, often over many years

A much rarer type of urticaria, known as urticaria vasculitis, can cause blood vessels inside the skin to become inflamed. In these cases, the weals last longer than 24 hours, are more painful, and can leave a bruise.

When to seek medical advice

Visit your GP if your symptoms don't go away within 48 hours.

You should also contact your GP if your symptoms are:

  • severe
  • causing distress
  • disrupting daily activities
  • occurring alongside other symptoms

Who's affected by urticaria

Acute urticaria (also known as short-term urticaria) is a common condition, estimated to affect around one in five people at some point in their lives.

Children are often affected by the condition, as well as women aged 30 to 60, and people with a history of allergies.

Chronic urticaria (also known as long-term urticaria) is much less common, affecting up to five in every 1,000 people in England.

What causes urticaria

Urticaria occurs when a trigger causes high levels of histamine and other chemical messengers to be released in the skin.

These substances cause the blood vessels in the affected area of skin to open up (often resulting in redness or pinkness) and become leaky. This extra fluid in the tissues causes swelling and itchiness.

Histamine is released for many reasons, including:

However, in many cases of urticaria, no obvious cause can be found.

Some cases of long-term urticaria may be caused by the immune system mistakenly attacking healthy tissue. However, this is difficult to diagnose and the treatment options are the same.

Certain triggers may also make the symptoms worse. These include:

Read more about the causes of urticaria.

Diagnosing urticaria

Your GP will usually be able to diagnose urticaria by examining the rash. They may also ask you questions to find out what triggered your symptoms.

If your GP thinks that it's caused by an allergic reaction, you may be referred to an allergy clinic for an allergy test. However, if you've had urticaria most days for more than six weeks, it's unlikely to be the result of an allergy.

You may also be referred for a number of tests, including a full blood count (FBC), to find out whether there's an underlying cause of your symptoms.

Read more about diagnosing urticaria.

Treating urticaria

In many cases, treatment isn't needed for urticaria, because the rash often gets better within a few days.

If the itchiness is causing you discomfort, antihistamines can help. Antihistamines are available over the counter at pharmacies - speak to your pharmacist for advice.

A short course of steroid tablets (oral corticosteroids) may occasionally be needed for more severe cases of urticaria.

If you have persistent urticaria, you may be referred to a skin specialist (dermatologist). Treatment usually involves medication to relieve the symptoms, while identifying and avoiding potential triggers.

Read about treating urticaria.

Complications of urticaria

Around a quarter of people with acute urticaria and half of people with chronic urticaria also develop angioedema, which is a deeper swelling of tissues.

Chronic urticaria can also be upsetting and negatively impact a person's mood and quality of life.

Angioedema

Angioedema is swelling in the deeper layers of a person's skin. It's often severe and is caused by a build-up of fluid. The symptoms of angioedema can affect any part of the body, but usually affect the:

  • eyes
  • lips
  • genitals
  • hands
  • feet

Medication such as antihistamines and short courses of oral corticosteroids (tablets) can be used to relieve the swelling.

Read more about treating angioedema.

Emotional impact

Living with any long-term condition can be difficult. Chronic urticaria can have a considerable negative impact on a person's mood and quality of life. Living with itchy skin can be particularly upsetting.

One study found that chronic urticaria can have the same negative impact as heart disease. It also found that one in seven people with chronic urticaria had some sort of psychological or emotional problem, such as:

See your GP if your urticaria is getting you down. Effective treatments are available to improve your symptoms.

Talking to friends and family can also improve feelings of isolation and help you cope better with your condition.

Read about how talking to others can help.



Causes of urticaria

Urticaria occurs when histamine and other chemicals are released from under the skin's surface, causing the tissues to swell.

Short-term (acute) urticaria

The triggers of acute urticaria are unknown in around half of all cases.

Recognised triggers include:

Long-term (chronic) urticaria

Chronic urticaria may occur when the body's immune system attacks its own tissues. This is known as an autoimmune reaction.

About a third to half of all chronic cases of urticaria are thought to be autoimmune related.

It's not known why autoimmune urticaria develops, although it can sometimes occur in combination with other autoimmune conditions, such as:

  • rheumatoid arthritis - when the immune system attacks the joints
  • lupus - when the immune system attacks the joints and skin, and people usually feel tired all the time

Chronic urticaria can also be linked to other chronic illnesses and infections, such as:

Chronic urticaria tends to come and go. Many people find that certain things make it reappear or make existing symptoms worse. Triggers sometimes include:

  • stress
  • alcohol
  • caffeine
  • warm temperatures
  • prolonged pressure on the skin - this can happen by wearing tight clothing
  • medications - such as NSAIDs, and the painkiller codeine
  • certain food additives - such as salicylates, which are found in tomatoes, orange juice and tea
  • insect bites and stings
  • exposure to heat, cold, pressure or water

ACE inhibitors that are often used to treat high blood pressure (hypertension) can be linked to deeper swellings of angioedema.

Diagnosing urticaria

Urticaria can usually be diagnosed by examining the distinctive red rash.

If you have long-term (chronic) urticaria, a number of tests may be needed to identify the underlying cause.

Short-term (acute) urticaria

Your GP can usually diagnose acute urticaria by examining the rash.

They'll also ask you some questions to find out what triggered your symptoms, including:

  • when and where the rash began
  • what you had to eat just before it began and details of your usual diet
  • if you started taking any new medication just before your symptoms began
  • if you live or work in an environment where you come into contact with possible triggers - such as pets, chemicals or latex gloves
  • if you were stung or bitten by an insect just before your symptoms started
  • your current state of health and if you've had any recent infections
  • if you've recently travelled to a foreign country and if so, where
  • if there's a history of urticaria in your family

In around half of all cases of acute urticaria, a cause can't be identified.

If your GP thinks your symptoms are caused by an allergic reaction, you may have to go to an allergy clinic.

Allergy testing may be needed to find out if you're allergic to suspected triggers for urticaria.

Long-term (chronic) urticaria

If your urticaria lasts for more than six weeks, it's very unlikely to be caused by an allergy, so allergy tests aren't usually recommended.

However, your GP should ask about anything that makes your urticaria worse, such as:

  • any medicines you're taking
  • your alcohol and caffeine consumption
  • your stress levels

You may also be referred for a number of tests to find out if there's an underlying cause of your chronic urticaria. These tests may include:

  • a full blood count test (FBC) - which can identify anaemia
  • tests to determine the levels of antibodies in your blood
  • a stool sample - which can identify intestinal parasites
  • an erythrocyte sedimentation rate (ESR) test - which can help to identify problems with your immune system
  • thyroid function tests - which can be used to check for an underactive thyroid gland (hypothyroidism) or an overactive thyroid gland (hyperthyroidism)
  • liver function tests - which can be used to check if you have any problems with your liver
Treating urticaria

Most cases of urticaria don't need treatment, because the symptoms are usually mild and often get better within a few days.

Short-term (acute) urticaria

If your symptoms are troublesome or persistent, antihistamines are available over the counter from pharmacies.

See your GP or speak to your pharmacist if your symptoms get worse. If your symptoms are very severe, your GP may prescribe other medications, such as a short course of corticosteroid tablets.

Go back to your GP if your symptoms get worse or if the treatment hasn't worked after two weeks.

Antihistamines

Antihistamines block the effects of histamine, helping to stop the itchiness and reduce the rash. Examples of antihistamines include:

  • cetirizine
  • fexofenadine
  • loratadine

For most people, modern antihistamines don't cause drowsiness, although there are some exceptions. See how you react to the antihistamine before driving or operating heavy machinery. Antihistamines may also cause drowsiness if taken with alcohol. Always read the information leaflet that comes with the medication.

Antihistamines aren't usually prescribed to pregnant women, as it's not known whether they're entirely safe. However, chlorphenamine may be recommended if it's believed that the benefits outweigh the risks. There's no evidence that chlorphenamine harms unborn babies.

Corticosteroid tablets

You may be prescribed a short course of high-dose corticosteroid tablets, such as prednisolone, if your symptoms are severe.

Corticosteroids suppress your immune system, which lessens the symptoms of urticaria. A course of prednisolone lasting between three and five days is usually recommended.

Taking steroid tablets on a long-term basis isn't usually recommended, because it can lead to a wide range of side effects and complications, such as:

Long-term (chronic) urticaria

Treatment for chronic urticaria involves trying to control your symptoms and avoiding any triggers that make them worse.

If you have chronic urticaria and angioedema, you may be referred to a skin specialist (dermatologist). This is because angioedema is potentially more serious and can cause breathing difficulties.

You should also be referred to a dermatologist if you just have chronic urticaria and the symptoms continue, despite treatment.

Antihistamines

Chronic urticaria is treated with antihistamines. You may have to take them regularly for as long as your symptoms last.

An increased dose may be recommended if your symptoms don't respond to treatment. Increasing the dose can often help to control symptoms that previously didn't respond to treatment. However, this should only be carried out under the instruction of the doctor in charge of your care.

Menthol cream

Menthol cream can be used as an alternative or in addition to antihistamines because it helps to relieve itchiness. Your GP can prescribe this.

Corticosteroid tablets

Occasionally, more serious episodes of urticaria can be treated with short doses of corticosteroid tablets, such as prednisolone. Possible side effects of corticosteroid tablets include:

Long-term use of corticosteroids for chronic urticaria isn't recommended for the reasons mentioned above.

H2 antihistamines

The type of antihistamines you can get from the pharmacist are known as H1 antihistamines. However, there are several other types of antihistamines, including H2 antihistamines.

H2 antihistamines can sometimes be useful for treating chronic urticaria, because they narrow blood vessels, which can reduce the skin's redness.

H2 antihistamines can be used as an alternative to H1 antihistamines or in combination with them. Side effects of H2 antihistamines are uncommon, but include:

Don't drive or use tools or machinery if you feel dizzy after taking a H2 antihistamine.

Leukotriene receptor antagonists

Leukotriene receptor antagonists are a type of medication that can help to reduce redness and swelling of the skin.

They can be a useful long-term alternative to using corticosteroid tablets, because they don't carry the same risk of causing wide-ranging side effects.

The side effects of leukotriene receptor antagonists are rare and relatively minor. They include headaches and nausea (feeling sick).

Ciclosporin

In around two-thirds of cases, a powerful medication called ciclosporin has proved effective in treating urticaria.

Ciclosporin works in a similar way to corticosteroids. It suppresses the harmful effects of the immune system and is available in capsule form or as a liquid.

Side effects of ciclosporin include:

There are also a number of other side effects that can occur when taking ciclosporin, and you should discuss these thoroughly with your doctor before starting.

Side effects, such as high blood pressure and high cholesterol, are a particular cause for concern, because they can increase your risk of heart disease and stroke.

Even if you still respond to treatment, it may be recommended that the medication is withdrawn after a few months.

Omaluzimab

For urticaria that hasn't responded to antihistamines, there are newer medications becoming available, such as omalizumab. Omalizumab is given by injection and is thought to reduce a type of antibody that can play a part in urticaria.

Diet

There's some uncertainty over the role of diet in people with long-term urticaria. There are two groups of chemicals in foods that may trigger urticaria in some people - vasoactive amines and salicylates.

The Allergy UK website has more information on:

Avoiding or cutting down on foods that contain these chemicals may improve your symptoms. You could also keep a food diary to see whether avoiding certain foods helps you.

However, you should talk to a dietitian before restricting your diet. They can make sure you're not avoiding foods unnecessarily and that your diet is healthy.

Avoiding triggers

If you know what triggers your urticaria or makes it worse, avoiding the trigger may keep your symptoms under control.

Triggers such as alcohol and caffeine can be easily avoided. If you think that a certain medication may be triggering your symptoms, contact the doctor who prescribed it, because alternatives may be available.

Avoiding stress can be more difficult, particularly if your symptoms negatively affect your quality of life.

If you have severe urticaria or urticaria that keeps coming back, you may find that relaxation techniques, such as meditation or hypnosis, reduce your stress levels and the severity of your symptoms.

 
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