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 things, including:
- Allergic reaction, for example 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.
- Physical triggers, such as pressure to the skin, low temperature, sunlight and water.
However, in about 50% of cases, no cause is identified.
Urticaria is a common condition, affecting one in six people at some point in their life. It is more likely to affect children and women.
The rash normally disappears after a few days, but some cases can last longer. It isn't 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 one in every 1,000 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 angioedema. Angioedema 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 angioedema see the Useful links.
Anaphylaxis
In rare cases urticaria can be 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 a life-threatening condition and needs emergency treatment.
