Urticaria (hives) is one of the most common skin reactions, affecting up to 20% of people at some point in their lives. The characteristic raised, itchy wheals (welts) appear suddenly and can disappear within hours — yet behind them lies a fascinating immunological reaction.
In this article, we explain exactly what urticaria is, what causes it, what it looks like, and what you can do about it.
What is urticaria (hives)?
Urticaria, commonly known as hives, is a skin condition characterised by suddenly appearing raised, itchy red wheals. Wheals occur when mast cells in the skin release histamine and other mediators locally into the surrounding dermis, so that the small blood vessels there dilate and leak fluid into the tissue.
The release is local — which is exactly why wheals are sharply defined and transient. In anaphylaxis the same mediators are released systemically throughout the body, and that is the crucial difference between an ordinary outbreak of hives and a life-threatening allergic reaction.
Urticaria is not contagious — you cannot pass it on to others. A single episode usually resolves within 24 hours, but new wheals may appear as old ones fade. When the condition persists for more than 6 weeks, it is classified as chronic urticaria.
What does urticaria look like?
Urticaria has a fairly distinctive appearance that sets it apart from other skin conditions:
- Raised, red wheals: The wheals can vary in size from a few millimetres to several centimetres and appear anywhere on the body. They are typically red at the edges with a pale centre.
- Intense itching: Itching is often the most bothersome symptom and can be very intense, particularly at night or in warm environments.
- Confluence: Multiple wheals can merge into larger, irregular, raised areas called plaques.
- Rapidly changing appearance: An individual wheal typically resolves within 1–24 hours without leaving a mark. However, new wheals may develop elsewhere on the body.
It is this rapid turnover that distinguishes urticaria from contact dermatitis, where the rash stays in the same place for days to weeks and often scales. If an individual lesion lasts more than 24 hours, hurts rather than itches, or leaves a bruise-like mark, it should be seen by a doctor.
In some cases urticaria is accompanied by angioedema — a deeper swelling beneath the skin, typically affecting the face, lips, tongue or throat. Angioedema requires immediate medical attention, especially when the throat is involved.
Why does urticaria happen?
Urticaria occurs when mast cells in the skin release histamine in response to a trigger. Triggers can be divided into three main categories:
Which allergens can trigger urticaria?
Food allergies — particularly nuts, shellfish, eggs and dairy — are common causes of acute urticaria. Medications such as penicillin and aspirin, insect bites and stings and pollen can also trigger a reaction. The body recognises these substances as foreign and mounts an immune response that releases histamine.
Can physical triggers cause urticaria?
Yes. The inducible (physical) urticarias are triggered by a specific physical stimulus rather than by an allergen. Dermographism is the most common: stroking, scratching or friction produces a linear wheal within minutes, which settles again within an hour.
Delayed pressure urticaria is a separate condition: sustained pressure from a waistband, a shoulder strap or a tool handle produces a deep, often tender swelling that appears only 4–8 hours after the pressure and can last a day or more. Other forms include cold urticaria (cold air, cold water or cold objects), heat urticaria (localised warming), solar urticaria (sunlight within minutes of exposure) and exercise-induced urticaria (a rise in body temperature during exertion). These forms are not allergic in the traditional sense but result from mast cells that respond over-sensitively to a physical stimulus.
What about infections, stress and chronic spontaneous urticaria?
Infections — such as colds, urinary tract infections or Helicobacter pylori — can trigger urticaria. Stress and underlying conditions such as autoimmune disease or thyroid disorders are other known factors. In more than 80% of chronic urticaria cases no external cause is found at all; these are termed chronic spontaneous urticaria. That is worth knowing before spending time and money on extensive allergy testing: in most people with chronic hives the tests come back normal.
Who gets urticaria?
Urticaria can affect anyone — regardless of age, sex or skin type. However, it is more common in adults than in children. Acute urticaria is most frequent in children and young adults and is most often triggered by an allergic reaction or infection. Chronic urticaria occurs most often in women aged 20–40 and can last months to years.
What can you do about urticaria?
Treatment of urticaria focuses on two tracks: relieving symptoms and identifying and avoiding the trigger.
Antihistamines (primary treatment)
Non-sedating antihistamines such as cetirizine and loratadine are the first-line treatment. They block histamine receptors and reduce itching and swelling. Regular dosing is more effective than taking them only when needed.
Identify the trigger
Keep a diary of diet, activities and outbreaks. Allergy testing (skin prick tests or blood tests) can identify specific allergens. Once the trigger is identified, avoidance is the most important preventive measure.
Prescription treatment (chronic urticaria)
When a standard dose of antihistamine is insufficient, a doctor may increase the dose of a non-sedating antihistamine to up to four times the standard dose. If that is still not enough, the biologic omalizumab (Xolair) is the next step and is approved for chronic spontaneous urticaria; ciclosporin is a further option in specialist care.
Anaphylaxis — seek immediate help
Throat swelling, breathing difficulty, dizziness or a drop in blood pressure may indicate anaphylaxis — a life-threatening allergic reaction. Call 112 (emergency services) immediately. If you are at risk, always carry an adrenaline auto-injector (EpiPen or Jext) and use it in the outer thigh at the first signs — and then still call 112, because the reaction can flare again hours later (a biphasic reaction).
Medical classification: Urticaria is classified as EB00 in the WHO's International Classification of Diseases (ICD-11), within the chapter on urticaria, angioedema and related disorders. It is characterised by transient, itchy wheals, often allergic or spontaneous in nature, with non-sedating antihistamines as the primary treatment.
Frequently asked questions
Is urticaria dangerous?
In most cases urticaria is harmless and resolves within hours to days. It can become dangerous if accompanied by angioedema of the throat or signs of anaphylaxis — call 112 immediately in those cases.
What is the difference between acute and chronic urticaria?
Acute urticaria lasts under 6 weeks and is usually caused by an identifiable trigger such as an allergen or an infection. Chronic urticaria lasts more than 6 weeks, and in more than 80% of cases no external cause is found (chronic spontaneous urticaria). Both forms are primarily treated with non-sedating antihistamines.
When should I contact a dermatologist?
Contact a dermatologist if urticaria lasts more than 6 weeks, if a standard dose of antihistamine is not providing adequate relief, or if the outbreaks are affecting your sleep and daily life. A dermatologist can judge whether you need a higher dose or treatment beyond antihistamines.
Get an assessment within 48 hours
If you have throat swelling, breathing difficulty or dizziness, call 112 — that cannot be assessed from a photo. For ordinary hives, upload photos of your skin via the SKIND app and receive a personal assessment and treatment plan from a certified dermatologist — no hospital waiting list.
Disclaimer: This article is for informational purposes only and does not replace professional medical advice. Always consult a doctor or dermatologist for personal guidance and assessment of skin changes.