Medically reviewed by Dr. A.M. van Coevorden, dermatologist
Hivesitchy welts that appear and fade again
Hives, also known as nettle rash or urticaria, is a skin rash of itchy welts that appear within a short time and usually fade within a few hours, always within 24 hours. The name comes from urtica, Latin for stinging nettle. Nearly a quarter of all people experience hives at some point in their lives, at any age and equally in men and women.
What are hives?
The rash starts as small red spots. These can develop into raised red or pale patches, and patches can merge into larger ones. Such a patch is called a wheal (urtica). If the whole episode lasts less than six weeks, it is called acute hives. This is usually the case. If it lasts longer than six weeks, it is called chronic hives.
What causes hives?
Histamine plays the central role. This substance is stored in mast cells, immune cells in the skin. Various triggers can release histamine. Histamine widens the blood vessels, making the skin red. It also makes the vessel walls more permeable to fluid, causing local swelling. And it causes itch.
Triggers that can release histamine:
- physical triggers such as exercise, pressure on the skin, cold, heat, sunlight, water or vibration (inducible urticaria)
- medicines, especially painkillers and antibiotics
- acute and chronic infections, mainly viral and parasitic
- food allergy, for example to peanuts, tree nuts, shellfish and fruit
- food additives such as colourings, preservatives and flavour enhancers
- insect stings and bites
- allergy to inhaled substances such as mould spores or animal dander
- contact allergies
- internal diseases
Sometimes several triggers act at once. Some triggers, such as physical stimuli and painkillers, can worsen existing hives. In chronic hives, no cause is found in 60 to 90% of people. This is called chronic spontaneous urticaria. There is no clear hereditary pattern, although hives run in some families, particularly the forms triggered by cold and sunlight.
What are the symptoms?
The typical wheal is an intensely itchy, raised red patch, often pale in the centre. Patches can grow and merge. Characteristically, they disappear within a few hours without leaving any mark on the skin. There is no preferred site: arms, legs, trunk and face are affected equally often. When an external trigger is involved, the patches usually appear where that trigger touched the skin. Pressure urticaria typically affects the knees, palms and soles; wheals from insect bites usually appear on the forearms and lower legs.
Special forms:
- Exercise-induced urticaria: pinhead-sized, itchy or burning red bumps triggered by sweating, physical exertion or a warm environment.
- Urticaria factitia: streak-shaped, itchy wheals after pressure or rubbing of the skin, also known as dermographism. It occurs to some degree in 3 to 5% of people.
- Cold urticaria: wheals where the skin cools down, for example when swimming in cold water. A widespread reaction with a drop in blood pressure and loss of consciousness can be dangerous, with a risk of drowning while swimming. The diagnosis can be confirmed with an ice cube test.
- Delayed pressure urticaria: painful, firm swellings that appear on pressure points after several hours, often around the joints. This form is sometimes mistaken for joint inflammation and is difficult to treat.
Are hives contagious?
No. Hives are caused by the release of histamine in your own skin and cannot be passed from person to person.
How is the diagnosis made?
Doctors usually recognise hives easily. Talking through the most common causes often identifies the trigger without further tests. Targeted investigation only follows when there are clues pointing to a specific cause.
What is the treatment?
The basis is avoiding the trigger, if it is known. If that is not possible, antihistamines are usually effective: modern medicines that block the action of histamine and generally do not cause drowsiness. A higher dose is often needed than for hay fever. If one antihistamine does not help enough, another can be tried. Montelukast can be added, a medicine normally used for exercise-induced asthma that can also work well for hives. For flare-ups, a doctor can prescribe a short course of prednisone. If sufficiently dosed antihistamines combined with montelukast do not give the desired result, omalizumab can be considered. This medicine removes the substances that activate the mast cells. If omalizumab does not work well enough or cannot be given, other medicines that suppress the immune system come into view, such as ciclosporin.
What is the outlook?
In most cases hives are short-lived, sometimes so short that the patches are gone before an appointment can take place. In some people, hives persist for longer and can last months to years.
Frequently asked questions about hives
Are hives contagious?
No. Hives are caused by the release of histamine in your own skin and cannot be passed from person to person.
How long do the welts last?
Individual patches usually fade within a few hours and always within 24 hours, without scars or marks. New patches can keep appearing, though.
Are hives an allergy?
Sometimes, for example with a food allergy or an insect sting. But in chronic hives, no cause is found in 60 to 90% of people.
What is the difference between acute and chronic hives?
Acute hives last less than six weeks in total; this is the most common form. Lasting longer than six weeks makes it chronic, which can persist for months to years.
What treatments are there?
First, avoiding the trigger if it is known, then antihistamines. If these do not help enough, there are next steps: montelukast, a short course of prednisone for flare-ups, omalizumab, and immune-suppressing medicines such as ciclosporin.