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Urticaria (Hives): Allergy Testing & Causes

Q: What is urticaria, and how does it differ from a normal allergic rash?

Urticaria is the medical term for hives — raised, itchy welts that appear on the skin when mast cells release histamine. Individual welts typically fade within 24 hours, though new ones may continue to appear. It is not a single condition: it can be acute or chronic, IgE-mediated or autoimmune, or triggered by physical stimuli such as cold, heat, pressure or exercise.

Q: What does it mean if my urticaria is chronic?

Hives that occur most days for six weeks or longer are classified as chronic urticaria. The most common form is chronic spontaneous urticaria (CSU), where no obvious external trigger is identified. A proportion of CSU cases have an autoimmune component. Discuss persistent hives with your GP, who may refer you to a dermatologist or allergy specialist.

Q: Is chronic urticaria caused by an allergy?

In most cases of chronic urticaria, a single food, drug or environmental allergy is not the cause. IgE blood testing can help rule out allergic triggers; for chronic spontaneous urticaria, the underlying mechanism is often autoimmune rather than allergic. Your healthcare professional can interpret testing in the context of your full clinical picture.

Q: What is a histamine-releasing test, and when is it useful?

This specialised blood test measures how readily your basophils (a type of white blood cell) release histamine when stimulated. It can provide additional context in the investigation of chronic urticaria, particularly when standard IgE testing is inconclusive. Results should be reviewed by a clinician.

Q: Do I need to stop antihistamines before a blood test?

No. Unlike skin prick testing, IgE blood tests and histamine-releasing tests are not affected by antihistamines. You can continue your usual medication before your appointment.

Q: What should I do with my results?

As a diagnostic-only clinic, we provide results directly to you. We recommend sharing them with your GP, dermatologist or allergy specialist for interpretation alongside your full clinical history.

An overview of urticaria types — IgE-mediated, autoimmune, physical and chronic spontaneous — and where blood testing fits in

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⚠️ When hives are an emergency — call 999

Urticaria can be a feature of anaphylaxis. Call 999 immediately and go to A&E if hives appear alongside any of the following: difficulty breathing, swelling of the lips, tongue or throat, persistent coughing or wheezing, dizziness, collapse, or a sudden drop in blood pressure. If an adrenaline auto-injector (e.g. EpiPen, Jext, Emerade) has been prescribed, use it as instructed before calling 999. For urgent but non-emergency advice, call NHS 111.

What Is Urticaria?

Urticaria — commonly called hives — is a skin reaction characterised by raised, itchy welts (wheals) that can vary in size and shape. The welts appear when mast cells in the skin release histamine and other inflammatory mediators, causing local fluid leakage from small blood vessels. Individual lesions typically come and go within 24 hours, though new ones may continue to appear in different locations.

Urticaria affects around 1 in 5 people at some point in life. In most cases the reaction is short-lived (acute urticaria), but in a smaller proportion it persists for six weeks or longer — at which point it is classified as chronic urticaria. When deeper tissues are involved and swelling extends below the skin surface, the condition is referred to as angioedema and may coexist with hives.

Although the visible rash is the same across most types, the underlying mechanism can vary considerably — which is why understanding the type helps guide whether blood testing or other investigations are likely to be informative.

The Main Types of Urticaria

Clinicians broadly group urticaria into the following categories. A single individual may experience more than one type.

1. Acute urticaria

Hives that resolve within six weeks. Often linked to an identifiable trigger such as a food, medication, viral infection or insect sting. IgE blood testing may help identify the specific allergen where one is suspected.

2. Chronic spontaneous urticaria (CSU)

Hives lasting six weeks or longer with no obvious external trigger. CSU is the most common form of chronic urticaria. In a proportion of cases an autoimmune mechanism is thought to play a role. See our dedicated chronic urticaria testing guide.

3. Chronic inducible urticaria

Hives consistently provoked by a specific physical stimulus, including:

→ Cold urticaria — triggered by cold air, water or surfaces
→ Heat urticaria — triggered by warm contact or environments
→ Cholinergic urticaria — triggered by a rise in core body temperature (exercise, hot showers, stress)
→ Dermographism — wheals appear where the skin is firmly stroked or scratched
→ Pressure, vibratory or solar urticaria — rarer physical subtypes

4. Autoimmune urticaria

A subset of chronic spontaneous urticaria where the immune system produces antibodies against its own IgE molecules or IgE receptors on mast cells, leading to persistent mast-cell activation. Investigation may involve histamine-releasing tests and thyroid antibody screening, typically arranged by a dermatologist or allergy specialist.

IgE-Mediated vs Autoimmune Urticaria

One of the most useful distinctions in urticaria is whether the reaction is being driven by an external allergen (IgE-mediated) or by the immune system targeting its own cells (autoimmune). The features below can help frame the picture, although only a clinician can interpret your individual case.

Feature	IgE-mediated urticaria	Autoimmune / chronic spontaneous urticaria
Typical onset	Minutes to hours after exposure	No clear time-link to exposure
Duration	Acute (< 6 weeks)	Chronic (6 weeks +)
Trigger	Identifiable allergen (food, drug, sting, latex)	No consistent external trigger
Specific IgE blood test	Often positive to suspected allergen	Usually negative
Histamine-releasing test	Less commonly relevant	May provide additional context
Associated conditions	Atopy: hay fever, eczema, food allergies	Autoimmune thyroid disease, vitiligo, other autoimmune conditions

Which Blood Tests May Be Relevant?

The right investigation depends on the type of urticaria suspected. Common options ordered through our nurse-led clinic include:

→ Specific IgE testing — useful when an allergen is suspected as a trigger for acute urticaria (foods, drugs, insect venom, latex)
→ Total IgE — provides a baseline that may be relevant when chronic urticaria is being investigated by a specialist
→ Histamine-releasing urticaria test — specialised assay that can support investigation of chronic spontaneous urticaria
→ ALEX² multi-allergen panel — broad screen across hundreds of allergens and components when the trigger is unclear
→ Eosinophil Cationic Protein (ECP) — a marker of allergic inflammation that may add context alongside IgE results

As a diagnostic-only service, we provide results directly to you. We recommend sharing them with your GP, dermatologist or allergy specialist for clinical interpretation and to inform appropriate next steps.

How Testing Works

Choose Your Test

Select from our range of allergy blood tests and book a convenient time at our South Kensington clinic. No GP referral needed.

Nurse Blood Draw

A qualified nurse takes a small blood sample at our clinic. The appointment is quick and straightforward.

Get Your Results

Results are sent directly to you, typically within a few working days. Share them with your GP or specialist to guide your next steps.

Tests Available at Our Clinic

Why Choose a Diagnostic-Only Clinic?

Unlike clinics that provide both testing and treatment, our nurse-led service focuses solely on accurate diagnostic testing. Because we don't offer treatments or prescriptions, there is no commercial incentive to recommend unnecessary tests — just honest, impartial results you can trust.

Nurse-Led & Impartial

Our qualified nurses collect your sample — we don't prescribe, treat, or have any reason to upsell.

Results You Own

Your results are sent directly to you. Take them to your GP or a specialist to discuss what's best for your situation.

You Stay in Control

Understand your allergy profile, then decide with your healthcare professional what steps to take next.

When to Seek Medical Advice

See your GP if hives:

→ Persist for more than a few days, or recur frequently
→ Are interfering with sleep, work or daily activities
→ Are accompanied by swelling of the face, eyelids or lips
→ Develop alongside a fever or other unexplained symptoms
→ Affect a young child for the first time

Your GP can decide whether referral to a dermatologist or allergy specialist is appropriate and may arrange further investigation. Blood testing through a private clinic is one option that can complement — not replace — clinical assessment.

⚠️ Call 999 immediately if hives appear alongside breathing difficulty, throat or tongue swelling, dizziness or collapse — these may be signs of anaphylaxis.

Acute Urticaria Testing →

Information and tests for hives lasting less than 6 weeks, often linked to a specific trigger.

Chronic Urticaria Testing →

Information and tests for persistent hives lasting 6 weeks or longer, including chronic spontaneous urticaria.

Cold Urticaria →

Hives triggered by cold air, water or surfaces — a physical urticaria subtype.

Heat Urticaria →

Hives triggered by warm contact, heated environments or rising body temperature.

Frequently Asked Questions

What is urticaria, and how does it differ from a normal allergic rash?

Urticaria is the medical term for hives — raised, itchy welts that appear on the skin when mast cells release histamine. Individual welts typically fade within 24 hours, though new ones may continue to appear. It is not a single condition: it can be acute or chronic, IgE-mediated or autoimmune, or triggered by physical stimuli such as cold, heat, pressure or exercise.

What does it mean if my urticaria is chronic?

Hives that occur most days for six weeks or longer are classified as chronic urticaria. The most common form is chronic spontaneous urticaria (CSU), where no obvious external trigger is identified. A proportion of CSU cases have an autoimmune component. Discuss persistent hives with your GP, who may refer you to a dermatologist or allergy specialist.

Is chronic urticaria caused by an allergy?

In most cases of chronic urticaria, a single food, drug or environmental allergy is not the cause. IgE blood testing can help rule out allergic triggers; for chronic spontaneous urticaria, the underlying mechanism is often autoimmune rather than allergic. Your healthcare professional can interpret testing in the context of your full clinical picture.

What is a histamine-releasing test, and when is it useful?