What is Urticaria (Hives)? Causes, Symptoms and Treatment

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 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 welts called wheals. These welts occur when cells in the skin release histamine and other chemical mediators into the bloodstream, causing the surrounding blood vessels to dilate and leak fluid into the skin tissue.

Urticaria is not contagious — you cannot pass it on to others. A single episode usually resolves within 24 hours, but new welts 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 welts: The welts 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 welts can merge into larger, irregular, raised areas called plaques.
Rapidly changing appearance: An individual weal typically resolves within 1–24 hours without leaving a mark. However, new welts may develop elsewhere on the body.

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:

Allergens

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.

Physical factors

Physical urticaria occurs in response to direct physical stimuli: pressure on the skin (dermographism), cold (cold urticaria), heat, sunlight (solar urticaria) or exercise. These forms are not allergic in the traditional sense but result from an oversensitive response in the mast cells.

Internal factors and idiopathic urticaria

Infections — such as colds, urinary tract infections or helicobacter pylori — can trigger urticaria. Stress and underlying medical conditions such as autoimmune diseases or thyroid disorders are other known factors. In up to 50% of chronic urticaria cases no clear cause can be identified — these are termed chronic spontaneous (idiopathic) urticaria.

Who gets urticaria?

Urticaria can affect anyone — regardless of age, sex or skin type. However, it is more common in adults than 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/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 antihistamines are insufficient, a doctor may prescribe higher doses, add an H2-antihistamine (e.g. ranitidine) or a biologic such as omalizumab (Xolair), which is approved for chronic spontaneous urticaria.

🚨 Anaphylaxis — seek immediate help

Throat swelling, breathing difficulty, dizziness or a drop in blood pressure may indicate anaphylaxis — a life-threatening allergic reaction. Call emergency services immediately. Always carry an adrenaline auto-injector (EpiPen) if you are at risk.

Medical classification: Urticaria is classified under 'Urticaria, angioedema and other urticarial disorders' in the WHO's International Classification of Diseases (ICD-11). It is characterised by transient, itchy wheals, often allergic or idiopathic in nature, with 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 — seek immediate medical help 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 infection. Chronic urticaria lasts more than 6 weeks and in many cases has no clear cause (idiopathic). Both forms are primarily treated with antihistamines.

When should I contact a dermatologist?

Contact a dermatologist if urticaria lasts more than 6 weeks, if antihistamines are not providing adequate relief, or if you want allergy testing. A dermatologist can determine the cause and tailor the best treatment plan.

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Disclaimer: This article is for informational purposes only and does not replace professional medical advice. Always consult a dermatologist for personal guidance.