Nettle rash

Nettle rash (also known as urticaria, hives, or welts) is a raised, red, itchy rash that appears on the skin. Urticaria happens when a trigger, normally an allergen (something that produces an allergic reaction) causes the body to release histamine - a protein in our body. Histamine causes tiny blood vessels, known as capillaries, to leak fluid. The fluid then gathers in our skin and causes a rash.

Urticaria can be triggered by many different things, including:

- allergic reaction - such as to certain foods, or stings from bees or wasps,
- skin coming into contact with something that irritates it, such as latex, chemicals, or nettles,
- medicines, commonly nonsteroidal anti-inflammatory drugs (NSAID), which are used to treat pain and fever, and ACE inhibitors, which are used to treat high blood pressure, and
- physical triggers, such as pressure to the skin, low temperature, sunlight and water.
However, for around 50% of cases, no obvious cause is identified.

Urticaria is common, affecting 1 in 6 people at some point their life. It is more common amongst children and women.

The rash normally disappears after a few days, but some cases can last longer. It is not contagious.

Urticaria that does not continue for more than six weeks is known as acute urticaria.

Chronic Urticaria

If episodes of urticaria last for more than six weeks it is known as chronic urticaria. Chronic urticaria is much rarer than urticaria, affecting 1 in every 1000 people.

The causes of most cases of chronic urticaria are unknown, but it is believed that a problem with the person's immune system is involved.

Around 50% of people with chronic urticaria, and 25% of people with acute urticaria, also get a related condition called angio-oedema. Angio-oedema involves swelling in the deeper layers of the skin.

The swelling causes a burning sensation and often occurs on the neck and face, the fingers and toes, and in men, the genitals. For more information on angio-oedema see the 'Related articles' section.

Anaphylaxis

In rare cases urticaria can be the one of the first symptoms of an extreme allergic reaction known as anaphylaxis. As the reaction progresses, the throat and airways swell, making breathing difficult and the person experiences a massive drop in blood pressure.

Anaphylaxis is life-threatening, and needs emergency treatment. For more information on anaphylaxis see the 'Symptoms' and Related articles' sections.

Urticaria is thought to be activated by a trigger that causes a release of histamine and other chemicals from under the skins surface. This causes inflammation and fluid to gather under the skin, causing wheals and the blood vessels to dilate. The trigger is unknown in approximately half of the cases of acute urticaria.

Known triggers include:

- Medicines - an allergic reaction to certain medicines can cause the urticaria rash. These medicines include NSAIDs such as aspirin and antibiotics.
- Foods - many foods have been found to cause this hypersensitive reaction, the most common are nuts, eggs, chocolate, citrus fruits, strawberries, shellfish and food additives.
- Infections - including colds and flu. Also hepatitis B, glandular fever and intestinal parasites have been linked.
- Irritants, causing local urticaria - some of these include latex, nettles, plants, chemicals and insect bites.
- Other physical triggers - can include heat, exercise, exposure to cold, pressure and rarely exposure to sunlight.
Chronic urticaria

Chronic urticaria is rarely activated by such triggers, but usually starts as an autoimmune response, where antibodies which usually fight bacteria and viruses, appear to cause histamine and other chemicals to be released under the skin, causing the same response as above. The reason for this is unknown.

In rarer cases, chronic urticaria can also be caused by other chronic illnesses and infections, such as thyroid disease, viral hepatitis, or intestinal parasites.

Chronic urticaria often comes and goes. Many people find there are certain factors that can make their chronic urticaria reappear. These include:

- stress,
- alcohol,
- caffeine,
- warm temperature,
- tight clothing, and
- medications, especially NSAIDs, codeine, and ACE Inhibitors.

The rash caused by urticaria is characterised by swellings, known as wheals, on the skin. They are typically pink or red, have a round or oval shape, and are itchy. They can range in size from a few millimetres to the size of a hand.

Individual wheals normally fade after a few hours, but can be replaced by new ones. The wheals can appear on just one part of the body, or across a large part of it.

Most episodes of urticaria peak between 8-12 hours, then stop after 24 hours. However some episodes can last for several days, or even several months. Episodes of urticaria that last for more than 6 weeks are known as chronic urticaria.

Anaphylaxis

If you have the symptoms of urticaria it is important to watch out for further symptoms that could indicate that you are having an anaphylaxis reaction. If you experience any of the symptoms below, dial 999:

- Swelling of the lips, tongue and the lining of the mouth and throat, that cause difficulty breathing,
- nausea and vomiting,
- skin feels cold and clammy,
- a rapid heart rate,
- feeling faint, and
sudden feeling of extreme anxiety.

DiagnosisAcute urticaria

Acute urticaria can usually be successfully diagnosed by examining the rash on your skin. Your GP will also want to find out what triggered the urticaria, so you can avoid it in future.

They will ask you:

- when and where the episode began,
- whether you live or work in an environment where you come into contact with any possible triggers, such as pets, chemicals or latex gloves,
- whether you've been taking any medicines,
- any recent travel,
- if you have had any previous illnesses,
- what foods you eat in your diet,
- whether you have be bitten by an insect, and
- whether there is any history of this condition in your family.

In 50% of cases, a cause is never identified, though the condition normally resolves itself in a few days and does not return.

If your GP strongly suspects that there is a clear link to an allergic substance, you may be referred to an allergy clinic. Allergy clinics can test your blood and skin to see if you are allergic to certain substances, such as food, dust mites or chemicals.

Chronic urticaria

If your urticaria persists for more than six weeks, it is extremely unlikely that it is due to an allergy, so allergy tests are normally not recommended.

However, your GP should ask about any factors that while not causing the chronic urticaria, can make it worse, such as medicines, your alcohol and caffeine consumptions, and levels of stress.

You may also be referred for the following tests, to see if there is any underlying causes of your chronic urticaria:

- a full blood count test which can identify anaemia,
- a stool sample which can identify intestinal parasites,
- a erythrocyte sedimentation rate (ESR) test, which can help identify problems with your immune system,
- thyroid function tests, which can check whether you have an over or under-active thyroid, and
- liver function tests, which can check whether you have any problems with your liver.

TreatmentAcute urticaria

Treatment for acute urticaria is normally not required, as the symptoms are mild, and the condition normally resolves itself within a few days, and does not come back.

If the symptoms are more serious, or the condition persists, your GP will give you antihistamines. Antihistamines block the effects of histamine, so should stop the symptoms of itchiness and reduce the rash.

Modern antihistamines do not cause drowsiness in most people, but there are some exceptions. You should see how you react to the antihistamine, before driving or operating heavy machinery. Modern antihistamine may cause drowsiness if taken with alcohol. You should always read the information leaflet that comes with your medication.

If you are having problems sleeping at night due your urticaria being particularly itchy, your GP may give you additional antihistamines that are known to cause drowsiness.

Antihistamines are normally not prescribed during pregnancy. This is because they have not been established as being entirely safe. However, your GP may recommend an antihistamine called chlorphenamine if he feels the benefits outweigh the risk.

There are several thousand known cases of pregnant women taking chlorphenamine, and there is no evidence that it has any harmful effects on an unborn baby.

If you symptoms are more severe you will be given a short course of high-dose oral corticosteroids. Corticosteroids suppress your immune system, and therefore, can suppress the symptoms of urticaria. It is not recommended to take corticosteroids for longer than 5 days, as they can increase the risk of you getting an infection.

You should return to your GP if the symptoms get worse, or there is no response to treatment after 2 weeks.

Chronic urticaria

Treatment for chronic urticaria involves helping you control your symptoms, and avoiding any triggers that can make the symptoms worse.

If you have chronic urticaria and angio-oedema, you should be referred to an immunologist (a specialist on the immune system), an allergist or a dermatologist (a specialist in skin conditions). This is because angio-oedema is potentially more serious, as it can cause breathing difficulties.
If you only have chronic urticaria, but the symptoms remain troublesome despite treatment, you should also be referred.

Treatment for the symptoms of chronic urticaria is antihistamines. You may have to take antihistamines for as long as the symptoms persist. As with acute urticaria, you may be given a combination of both 'drowsy' and 'non-drowsy' antihistamines to aid sleep.

Menthol cream can also be used an alternative, or addition, to antihistamines, as it has been shown to relieve itchiness.

More serious episodes of urticaria can be treated with short doses of corticosteroids.

Avoiding triggers

If you have chronic urticaria it is important to recognise and avoid triggers, which can make symptoms worse.

Triggers such as alcohol, caffeine, and medication can be easily avoided. Avoiding stress can be harder, particularly if your symptoms are having an adverse effect on your quality of life.

Many people with chronic urticaria have found that studying relaxation techniques such as mediation, or hypnosis, have helped reduce both their stress levels and the severity of their symptoms.

You should also monitor the effect of skin creams, soaps, and detergents as they might make your symptoms worse. Hypoallergenic lotions and soaps (designed to contain as few potential allergic substances as possible) may help.

Diet

There is a controversy over the role of diet in people with chronic urticaria. One study has suggested that avoiding certain foods that can cause the body to produce histamine may help control symptoms, as while these foods may not trigger urticaria, they may make the condition worse.

Other experts have said the study were too small, and not carried out for long enough, to prove that this was the case.

You may wish to keep a food diary, to see if avoiding a certain food helps your symptoms.

Foods that are known to cause the production of histamine include:

- spinach,
- yoghurt,
- fish,
- tomato products,
- processed meats,
- strawberries, and
- chocolate.

ComplicationsAcute urticaria

Around 25% of people with acute urticaria, will also develop acute angio-oedema at the same time. Acute angio-oedema will normally resolve within 3 days. However, you should dial 999 if you start having difficulties breathing.

Angio-oedema can be treated with antihistamines and oral corticosteroids. See the 'Related articles' section for more information on angio-oedema.

Chronic urticaria

50% of cases of chronic urticaria will resolve within 3-5 years. 25% of the cases will persist for more than 10 years.

Living with a chronic condition for a significant amount of time can be frustrating and distressing, and around 15% of people with chronic urticaria have reported feelings of depression.

If you feel very low for more than a couple of weeks, feel as though you cannot cope, or feel suicidal, always see your GP as soon as possible.

If you need someone to talk to out of hours, you can call NHS Direct on 0845 46 47 or The Samaritans on 08457 90 90 90.

Your GP will be able to advise you about the types of help that are available, such as antidepressant medications and counselling.

There is also additional support from the NHS for people living with chronic conditions. See the 'Related articles' section for more information.

No info NHSDEC07