What causes unexplained hives?

Hives (urticaria) have many potential causes. Acute urticaria (lasting less than 6 weeks) is most commonly caused by a new food or drug trigger, infection, or insect sting. In about 50% of acute cases, an IgE-mediated allergic cause can be identified with testing. Chronic urticaria (lasting more than 6 weeks) is more complex and in the majority of cases is autoimmune or idiopathic rather than allergic — however allergy testing may still be useful to rule out a persistent allergen exposure.

Angioedema is swelling in the deeper layers of the skin, most commonly affecting the lips, eyelids, tongue, throat, hands and feet. When it occurs alongside urticaria (hives), it is usually allergic or autoimmune in origin. When it occurs without urticaria — particularly affecting the face, throat or bowel — hereditary or acquired angioedema (related to complement deficiency) should be considered, and this requires specialist investigation.

When should I get allergy testing for hives?

Allergy testing is most useful in acute urticaria where there is a suspected trigger (a new food, drug or insect sting around the time of the reaction). It is also helpful if you have recurrent episodes and want to identify whether a specific allergen is involved. ALEX3 can screen 300+ allergen components in one test, making it an efficient first-line investigation. If testing does not identify a cause and symptoms persist, referral to a specialist allergy clinic is appropriate.

Can antihistamines hide an allergy?

Antihistamines suppress histamine-mediated symptoms (hives, itching, runny nose) without affecting underlying IgE sensitisation. They do not prevent you from having a positive allergy blood test — IgE levels in the blood are not altered by antihistamine use. However, antihistamines should be stopped at least 3–5 days before a skin prick test if one is planned.

Allergy Testing · Skin Reactions

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Urticaria and Angioedema: What They Are

Urticaria (hives) presents as raised, itchy welts on the skin that can appear anywhere on the body. Individual wheals typically resolve within 24 hours but new ones may keep appearing. Urticaria is classified as:

Acute urticaria: Episodes lasting less than 6 weeks. Most commonly triggered by foods, drugs, infections, or insect stings. IgE-mediated allergy is the cause in a significant proportion of acute cases.
Chronic urticaria: Episodes persisting beyond 6 weeks. More often autoimmune or idiopathic in origin. Allergy testing may still be indicated to rule out ongoing allergen exposure.

Angioedema is swelling of the deeper skin layers, typically affecting the lips, eyelids, tongue, and throat. When it occurs together with urticaria, an allergic or autoimmune mechanism is most likely. Angioedema occurring without urticaria — especially repeatedly, or affecting the throat and bowel — may indicate hereditary angioedema, a different and more complex condition requiring specialist investigation.

Seek emergency care immediately if you develop throat swelling, difficulty swallowing, hoarseness, or any difficulty breathing. These may indicate anaphylaxis or severe angioedema and require urgent treatment.

When Urticaria Points to Allergy

An allergic cause is more likely when:

The reaction appeared within minutes to 2 hours of eating, taking medication, or being stung
Reactions are reproducible with the same exposure
You have other atopic conditions (asthma, eczema, hay fever)
Hives are accompanied by other allergic symptoms (runny nose, itchy eyes, swelling)

Common allergic triggers include foods (peanut, tree nuts, shellfish, fish, milk, egg, wheat), medications (penicillin, NSAIDs), and insect venom. Latex allergy can also present with urticaria on contact.

How ALEX3 Helps

ALEX3 tests IgE against 300+ specific allergen components in a single blood draw. For patients with hives or swelling of unknown cause, it provides an efficient and comprehensive screen — covering foods, environmental allergens, and insect venoms in one test.

Compared to ordering multiple individual RAST tests based on guesswork, a single ALEX3 panel:

Covers a broad range of potential triggers systematically
Identifies the specific molecular components involved, not just the allergen source
Helps distinguish genuine sensitisation from clinically irrelevant IgE findings
Guides an elimination trial or referral to specialist allergy services

Important: ALEX3 tests for IgE-mediated allergy only. It does not diagnose urticaria caused by autoimmune mechanisms, physical factors (cold, pressure, heat), or idiopathic causes. Your GP will help interpret results in the context of your clinical history.

Managing Urticaria While Awaiting Test Results

Non-sedating antihistamines (such as cetirizine or loratadine) are the mainstay of urticaria management. Antihistamines do not interfere with blood-based IgE testing (ALEX3), so they can be continued while awaiting results. If you are planning a skin prick test, antihistamines should be stopped 3–5 days beforehand.

If you have previously experienced severe allergic reactions, your GP may prescribe an adrenaline auto-injector (EpiPen or Jext) for emergency use while the investigation is under way.

Book Allergy Testing at Lambert Medical

If you have had unexplained hives, rashes or swelling, ALEX3 allergy testing provides a comprehensive first-line investigation at our Surbiton practice. Your GP will review results with you and advise on next steps.

Book ALEX3 Testing Allergy Testing Service

Frequently Asked Questions

Acute urticaria (under 6 weeks) is most often caused by a new food, drug, infection or insect sting trigger. About 50% of acute cases have an identifiable IgE-mediated allergic cause. Chronic urticaria (over 6 weeks) is more often autoimmune or idiopathic, though ruling out an ongoing allergen exposure is still worthwhile.

Angioedema is swelling in the deeper layers of skin, typically affecting the lips, eyelids, tongue, throat, hands and feet. With urticaria, it is usually allergic or autoimmune. Without urticaria, especially if recurrent, hereditary or acquired angioedema (complement-related) should be considered and requires specialist assessment.

Testing is most useful in acute urticaria with a suspected trigger, or in recurrent episodes where you want to identify an allergic cause. ALEX3 screens 300+ components in one test, making it an efficient first-line investigation. If no cause is found and symptoms persist, referral to a specialist allergy clinic is appropriate.

Antihistamines suppress histamine-mediated symptoms without affecting IgE levels in the blood. They will not interfere with ALEX3 blood testing. However, antihistamines should be stopped at least 3–5 days before a skin prick test if one is planned.

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Foods, inhalants, venoms
Component-level testing
GP-reviewed results
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Get to the Bottom of Your Hives

ALEX3 allergy testing screens 300+ components in a single blood draw — an efficient way to identify whether an allergen is driving your symptoms.