When hay fever spreads beyond pollen season or antihistamines stop controlling it, something has changed — and managing it as simple seasonal allergy is no longer enough.
June 2026 · 8 min read · Lambert Medical Clinical Team
Hay fever is supposed to be seasonal. It arrives when the pollen does, you take your antihistamines, and it retreats when the pollen season ends. But for a significant number of people, it doesn't work that cleanly — symptoms persist through autumn and winter, antihistamines lose their effect, and the runny nose and congestion become an almost permanent fixture.
This is not "bad" hay fever. It is a different clinical picture that needs a different approach.
Hay fever tends to worsen because of two interconnected processes: polysensitisation and priming.
When someone first develops hay fever, they are typically sensitised to one or two allergens — perhaps grass pollen and birch tree pollen. Over years of repeated exposure, the immune system can develop additional sensitivities. A person who started with purely seasonal grass pollen allergy may progressively add tree pollen sensitivity (extending symptoms into spring), then mould sensitivity (extending into autumn), and eventually house dust mite sensitivity — which is present year-round.
At this point, the pattern has fundamentally shifted from seasonal hay fever to perennial allergic rhinitis — year-round nasal allergy. But many patients (and some GPs) continue managing it as simple seasonal hay fever, which means the treatment never fully addresses what's driving the symptoms.
The nasal mucosa is not a passive filter. Chronic allergic inflammation changes it over time. A phenomenon called nasal priming occurs, in which repeated allergen exposure leaves the airways in a persistently inflamed state. In a primed nose, it takes a much smaller amount of allergen to trigger symptoms than it did originally — and the response is more severe.
This is why hay fever patients often notice that their first season in a new location feels mild, but by year three in the same place their symptoms are significantly worse, despite identical pollen levels. The pollen hasn't changed — the airway has.
Allergic rhinitis and asthma share the same underlying inflammatory mechanisms, and are increasingly understood as manifestations of the same disease in different parts of the airway. Around 20–30% of people with allergic rhinitis will develop asthma. If your hay fever is worsening and you've noticed chest tightness, wheeze, or breathlessness during pollen season or exercise, this warrants assessment — uncontrolled allergic rhinitis is a significant driver of difficult-to-control asthma.
True pharmacological tolerance to antihistamines is uncommon. More often, when antihistamines "stop working", it's because the clinical situation has changed:
History
Investigation
NICE guidelines place intranasal corticosteroids (such as fluticasone, mometasone, or beclomethasone nasal sprays) above antihistamines for moderate-to-severe allergic rhinitis. They reduce nasal inflammation directly rather than blocking histamine, and are more effective for congestion and nasal blockage — symptoms that antihistamines barely touch. Many patients use antihistamines as their main treatment but have never tried a nasal steroid spray, which often provides better overall symptom control.
They need to be used correctly and consistently — at least 2 weeks before pollen season and daily throughout. Most patients who "tried a nasal spray and it didn't help" had not used it for long enough or had not been shown the correct technique.
For moderate-to-severe hay fever, NICE recommends a combination approach: a regular intranasal corticosteroid plus an antihistamine taken as needed for breakthrough symptoms. Adding an intranasal antihistamine (such as azelastine) to a corticosteroid spray produces faster onset and better overall control than either alone.
A single injection of triamcinolone acetonide (Kenalog) can suppress allergic symptoms for 4–8 weeks during peak pollen season. It is not available on the NHS but is offered privately. It is most useful for patients with severe, uncontrolled symptoms or those in whom daily medication is not practical. It is not a treatment for year-round symptoms and is not suitable as a repeat annual injection due to cumulative steroid effects.
Read more in our Hayfever Injection guide.
Allergen immunotherapy (desensitisation) is the only treatment that targets the underlying allergy rather than masking symptoms. It involves controlled exposure to the allergen — either as sublingual tablets/drops or injections — in gradually increasing doses over 3–5 years. Over time, the immune system shifts from an allergic (Th2) response to a tolerant (Th1/regulatory) response.
Cochrane reviews of sublingual grass pollen immunotherapy show a significant reduction in symptom scores and medication use compared to placebo, with benefits persisting 3 years after stopping treatment. NICE has approved sublingual grass pollen immunotherapy for adults with seasonal allergic rhinitis that has not been adequately controlled by antihistamines and nasal corticosteroids.
To be eligible, you need a confirmed allergen profile from molecular testing. A standard blood test that shows you are "positive to grass pollen" is not specific enough — the immunotherapy product must match your exact molecular sensitisation.
Our ALEX3 molecular allergy test screens 300 allergens — including individual grass, tree and weed pollen molecules, house dust mite, pet dander, and moulds — from a single blood draw. No antihistamine withdrawal required. Results reviewed with a GP in a dedicated follow-up appointment.
If your "hay fever" symptoms are worse in bed, first thing in the morning, or in winter — or if you notice them especially around carpets or soft furnishings — house dust mite allergy is likely involved. House dust mites are microscopic arachnids that live in bedding, mattresses, carpets, and upholstered furniture. They are one of the most common allergens in the UK and a major cause of perennial (year-round) allergic rhinitis and asthma.
Standard hay fever treatment — pollen avoidance strategies, pollen-specific antihistamines — will have no effect on house dust mite symptoms. Identifying it requires specific allergy testing. Molecular testing can distinguish sensitisation to Der p 1 and Der p 2 (the main house dust mite allergens) from cross-reactive proteins, which affects both the severity assessment and treatment decisions.
If house dust mite is confirmed, the management approach is different: encasement of mattresses and pillows in allergen-proof covers, regular hot washing of bedding, and consideration of house dust mite sublingual immunotherapy, which is licensed in the UK.
Molecular ALEX3 test covering 300 allergens — pollen, dust mite, moulds, pets and more. GP review of results included.
£295 all-inclusive
Book NowYear-round symptoms may indicate house dust mite or pet dander allergy on top of pollen.
The ARIA guidelines classify rhinitis by duration and severity — and recommend different treatments for each.
Mild Intermittent
Antihistamine as needed
Moderate–Severe Intermittent
Intranasal steroid + antihistamine
Persistent (any severity)
Full investigation + consider immunotherapy