Think you need an allergy test? How doctors diagnose chronic spontaneous urticaria (CSU)
For many, recurring hives come with one question: "What's causing them?" While allergies are a common assumption, they aren't the only explanation. Dermatologist Dr Kok Wai Leong explains how doctors investigate recurring hives, when allergy testing may be useful and how patients can help reach the right diagnosis sooner.
When patients with recurring hives first see Dr Kok Wai Leong, Dermatologist and Co-founder of Dermatology Collective Clinic & Surgery, many arrive convinced they have an allergy.
It's an understandable assumption. Hives are raised, itchy bumps that may be red or skin-coloured and can turn white in the center when pressed. Because hives from different causes often look alike, it can be difficult to determine the underlying cause without a proper assessment.1 Naturally, many patients therefore expect an allergy test to provide the answer.
That may not always be the case. According to Dr Kok, consultations with the dermatologist usually begin with something much simpler: understanding the story behind the hives.
What patterns are dermatologists looking for
Rather than looking at one flare-up in isolation, dermatologists consider the pattern of symptoms. That means asking questions like:
- When did the hives first appear?
- How often do they return?
- Have they continued for six weeks or longer?
- Do they consistently appear after a particular food, medicine or other exposure?
- Do they occur without an obvious trigger?
These answers help distinguish between possible causes. Allergic reactions are usually linked to a specific trigger and tend to occur shortly after exposure.2 Hives that recur unpredictably without a clear trigger may instead point to chronic spontaneous urticaria (CSU), a chronic skin condition marked by recurring hives and/or swelling lasting six weeks or more, often without a clear trigger.1
How is CSU diagnosed
There is no single test that confirms CSU. Diagnosis is based primarily on a careful clinical history and physical examination, alongside consideration of other conditions that may cause similar symptoms. This is sometimes described as a diagnosis of exclusion.1
Further investigations may be considered if the history or examination suggests another cause or an associated condition. However, not every patient requires extensive testing.
The assessment also goes beyond the visible rash. Dr Kok asks how symptoms affect sleep, work, school and other aspects of daily life. Disrupted sleep and the impact on everyday activities are important indicators of disease burden and help guide treatment decisions.3
What if the symptoms disappear before your appointment
Hives are fleeting, explains Dr Kok. Patients may have a significant flare-up earlier in the day, only for the symptoms to disappear before they arrive at the clinic. Because hives come and go, they are often not visible during the consultation, making diagnosis more challenging.4
Information recorded outside the clinic is valuable. During each flare-up patients can:
- Take a clear photo of the hives when they appear, including both a close-up and the wider area affected.
- Keep a symptom diary. Record when your hives occur, how long they last, whether swelling develops, and how symptoms affect your sleep or daily life.
Photographs help your dermatologist assess what the rash looks like, while a symptom diary provides a clearer picture of how it behaves over time. Together, they can reveal patterns that may not be obvious during a single consultation.
Remember, early recognition is not only important for reaching a diagnosis, but also for ensuring symptoms are adequately controlled, particularly if hives or swelling continue to affect daily life despite treatment.
Where does allergy testing fit in?
Many patients expect an allergy test to provide the answer, but according to Dr Kok, whether allergy testing is helpful depends on what your symptoms suggest.
A positive allergy test alone does not necessarily explain why someone has recurring hives.4 Instead, the results need to be interpreted alongside your medical history and the pattern of your symptoms.
Only after your doctor has assessed the overall clinical picture can they decide whether allergy testing or other investigations are likely to be helpful.
What happens after diagnosis?
Recurring hives can be frustrating, but they aren't something you simply have to live with. Getting the right diagnosis is an important first step towards finding the care and treatment that's right for you.
If your symptoms are consistent with CSU, your dermatologist can discuss treatment options based on the severity of your condition, how it affects your daily life and your treatment goals. Reaching the right diagnosis also helps rule out other conditions that can present in a similar way.
Whether you are still looking for answers or have already been diagnosed with CSU, speak openly with your doctor about how often your symptoms occur and the impact they have on your sleep, work and daily life. This can help you and your doctor make more informed decisions about your care.
As Dr Kok emphasises, CSU is treatable.⁴ With the right care, the goal should be more than simply coping with recurring hives, but working towards optimising control of the condition and reducing disruption to your daily life.³
Dr Kok Wai Leong is a Dermatologist and Co-founder of Dermatology Collective Clinic & Surgery. He has a clinical interest in inflammatory and immunological skin conditions, including chronic spontaneous urticaria (CSU), eczema, psoriasis and allergic skin diseases. A former Visiting Consultant at Khoo Teck Puat Hospital and the National Skin Centre, Dr Kok is actively involved in dermatology research and medical education, and is committed to helping patients make informed decisions through evidence-based, personalised care.
THIS ARTICLE IS WRITTEN IN COLLABORATION WITH #ISEEU, AN INFORMATIONAL AND EDUCATIONAL WEBSITE ABOUT CHRONIC SPONTANEOUS URTICARIA (CSU).
Sources
- Zuberbier T, Ansari ZAH, Abdul Latiff AH, et al. The international guideline for the definition, classification, diagnosis and management of urticaria. Allergy. 2026;1-51. doi: 10.1111/all.70210
- Santos AF, Riggioni C, Agache I, et al. EAACI guidelines on the diagnosis of IgE-mediated food allergy. Allergy. 2023;78:3057-3076. doi:10.1111/all.15902.
- Weller K, Winders T, McCarthy J, Raftery T, Saraswat P, Constantinescu C, Balp MM, Bernstein JA. Urticaria Voices: Real-World Experience of Patients Living with Chronic Spontaneous Urticaria. Dermatol Ther (Heidelb). 2025 Mar;15(3):747-761. doi: 10.1007/s13555-025-01348-8. Epub 2025 Feb 28. PMID: 40019716; PMCID: PMC11909366.
- Friedman A, Kwatra SG, Yosipovitch G. A practical approach to diagnosing and managing chronic spontaneous urticaria. Dermatol Ther (Heidelb). 2024 Jun;14(6):1371-1387. doi: 10.1007/s13555-024-01173-5
