Part of the London Allergy Clinic
Diagnosis & Specialist Care of Allergy & Clinical Immunology - Since 1982
If you have had hives for weeks or months and nobody can tell you why, this page is for you. Chronic spontaneous urticaria — often shortened to CSU — is the most common form of long-lasting hives. "Chronic" means the hives have been coming and going for six weeks or more. "Spontaneous" means they appear without any identifiable trigger.That second word causes most of the distress, so it is worth being clear about what it actually means.
"Spontaneous" does not mean unexplained
Many people arrive at an appointment having spent months searching for a cause. They have kept food diaries, cut out dairy, changed their washing powder, replaced their bedding. Often they arrive apologetic, convinced they have missed something obvious.They usually haven't.In chronic spontaneous urticaria, there is no external trigger to find, because the process driving the hives is happening inside the immune system rather than in response to something you have eaten, touched or breathed in. The diagnosis is not a failure to find an answer. It is the answer.
What is actually happening
Hives appear when mast cells — immune cells sitting throughout the skin — release histamine and other inflammatory chemicals. Histamine makes blood vessels widen and leak fluid, producing the raised, itchy weals you can see and the itch you can feel.
In an allergic reaction, something from outside sets that process off. In chronic spontaneous urticaria, the mast cells are being activated from within. Research suggests that in a substantial proportion of people with CSU — by some estimates around half — the immune system produces antibodies that activate mast cells directly. It is an autoimmune process rather than an allergic one.
This is why allergy tests often come back clear in people with CSU, and why that clear result is not a disappointment. It is consistent with the diagnosis.
It also explains a connection that surprises many patients: up to 30% of people with chronic spontaneous urticaria also have an underactive thyroid, which is itself usually autoimmune. This is why thyroid function is often checked as part of the assessment.
Why cutting out foods rarely helps
This is one of the most useful things to understand early, because it can save months of unnecessary restriction.Food allergy causes hives that appear within minutes of eating, reliably, every time that food is eaten. If you can eat something on Monday without incident and it appears to cause hives on Thursday, that pattern points away from allergy rather than towards it. Chronic spontaneous urticaria fluctuates naturally. It flares and settles for reasons that often have nothing to do with what you have just eaten. When a flare happens to follow a meal, the connection feels obvious — but across weeks, the pattern usually does not hold up.None of this means you have been foolish to look. Looking for a cause is a reasonable response to an unexplained rash. It simply means that in CSU, the search is unlikely to be the thing that helps.
How common is it, and who gets it
Urticaria in some form affects around one in five people at some point in their lives. Chronic spontaneous urticaria is much less common, affecting somewhere in the region of 0.5% to 1% of people at any given time — still several hundred thousand people in the UK.It is roughly twice as common in women as in men, and can begin at any age, though it most often appears in adults between 20 and 40.
How long does it last?
This is usually the first question people ask, and the honest answer is that it varies.For most people, chronic spontaneous urticaria resolves on its own — but it can take time. The average duration is somewhere between two and five years. Around one in five people find it persists beyond five years.That is a long time to live with an unpredictable, itchy rash, which is why treatment matters rather than simply waiting it out.
The impact is real
Chronic urticaria is not a trivial condition, and it is often underestimated — sometimes by the people living with it.More than 40% of patients report that it significantly affects their daily functioning. Sleep is frequently disrupted, because itching tends to be worse at night. Anxiety is reported in a substantial proportion of patients. Research consistently finds the impact on quality of life comparable to conditions that are generally taken far more seriously.Stress does not cause chronic spontaneous urticaria. But it can reliably make it worse, which creates a difficult loop — the condition causes stress, and stress worsens the condition.
How it is diagnosed
Diagnosis is primarily clinical. Your consultant will take a detailed history: how long the hives have been present, how long individual weals last, whether there is swelling alongside them, what makes them better or worse, and what has already been tried.One detail matters more than most. Individual weals in urticaria usually fade within 24 hours, even though new ones keep appearing elsewhere. If individual spots last longer than that, bruise, or leave marks behind, that points towards a different diagnosis and changes the assessment.Blood tests are usually limited and targeted rather than extensive. Thyroid function is commonly checked. Testing for a wide range of allergens is generally not helpful in CSU and can produce misleading results, so a specialist will often recommend fewer tests rather than more.Please don't stop any medication before speaking to us. Many people with CSU are taking antihistamines to keep symptoms under control, and there is no need to stop them before an appointment. Blood tests are completely unaffected by antihistamines. Skin prick testing is rarely part of a CSU assessment, and if it were ever needed, your consultant would discuss the timing with you first.
Treatment
Treatment follows a well-established stepwise approach, reaffirmed in the 2026 international urticaria guideline supported by the British Society for Allergy and Clinical Immunology.
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Step one: non-sedating antihistamines.
A standard daily dose of a second-generation antihistamine, taken regularly rather than only when symptoms appear. Taken consistently, this controls symptoms adequately for a meaningful proportion of people.
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Step two: increasing the dose.
If a standard dose is not enough, guidelines support increasing it — up to four times the usual amount, under medical supervision. This is a well-established, evidence-based step, and many people who assume antihistamines don't work for them have never tried them at the doses the guidelines recommend.
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Step three: omalizumab.
For people whose symptoms remain uncontrolled despite optimised antihistamines, omalizumab is the recommended next treatment.
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Step four: ciclosporin.
For the smaller number who do not respond to omalizumab, ciclosporin may be an option under specialist supervision.
When antihistamines are not enough
Omalizumab, sold as Xolair, is a biological therapy given as an injection every four weeks. It binds to free IgE in the bloodstream, which reduces the sensitivity of mast cells and interrupts the cycle of histamine release.It is recommended by NICE for severe chronic spontaneous urticaria in adults and young people aged 12 and over whose symptoms have not responded to standard antihistamine treatment. For many people who had been told there was nothing more to try, the improvement is substantial.
A biosimilar version, Omlyclo, has demonstrated equivalent clinical efficacy and is also available.Our consultant, Dr Gururaj Arumugakani, has worked with omalizumab for chronic urticaria since before it received European licensing approval for that use. He is co-author of a published study of 357 patients treated over ten years, which found that adjusting omalizumab doses to the individual — rather than keeping everyone on the same fixed regimen — allowed 22% of partial responders to achieve full symptom control who would otherwise have remained undertreated. He also helped pioneer home therapy, the approach that allows most patients to self-inject at home after their first clinic doses.
Read more about omalizumab treatment
If it might not be urticaria
Not every persistent itchy rash is urticaria, and one condition is mistaken for it more often than any other. Eczema can look similar at a glance, but it behaves differently — it tends to stay in the same places, the skin becomes dry and thickened over time, and individual patches last far longer than a day.The distinction matters, because the treatments are entirely different. Our sister clinic has a guide to telling urticaria and eczema apart. We see urticaria and angioedema in adults and children, but we do not treat adult eczema — if that turns out to be the picture, we will say so and point you towards dermatology rather than take you through an assessment that won't help.
When to see a specialist
It is worth arranging a specialist assessment if:
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Hives have been present for six weeks or more
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If antihistamines are not giving adequate control
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If there is swelling alongside the rash, or
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If symptoms are affecting your sleep, work or day-to-day life.
You do not need to have exhausted every option first, and you do not need to arrive with an explanation. Not knowing why it is happening is the normal starting point for this condition.
Not sure what's causing your hives — or what to do next? Book a free 10-minute call with our team at The London Allergy Clinic and we'll help you work out the right next step.
Frequently Asked Questions
Speak to an urticaria specialist
You don't need to know what's causing it. Not knowing is the normal starting point.
The Urticaria & Hives Clinic is part of The London Allergy Clinic, which has provided specialist allergy and immunology care since 1982. Your consultation is up to an hour with a consultant — long enough to take a proper history, work out what's actually going on, and leave with a plan. No GP referral is needed.
Marylebone (all ages) · Fitzrovia (18+) · High Barnet (12+) · or by secure video
Mon–Sat, 9am–7pm ·
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