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Updated March 16, 2026 - Allergen immunotherapy, a treatment once sidelined due to safety concerns, is gaining renewed attention as a potential long-term solution for seasonal allergies.
Revisiting an old treatment
Forty years ago, allergist Glenis Scadding treated a patient whose severe hay fever made even short walks unbearable. Using sublingual immunotherapy-drops of birch pollen extract placed under the tongue-she helped desensitize him to the allergen. The patient's gratitude was immediate: he arrived at her home with a case of wine, celebrating his newfound ability to enjoy spring without wheezing.
Scadding, now vice president of the nonprofit Euforea and an honorary consultant at University College Hospital London, recalls the backlash she faced for the treatment. "I got so much flack, I stopped," she says. Yet today, the approach is regaining credibility as a safer alternative to traditional allergy shots.
The burden of seasonal allergies
Allergic rhinitis, commonly known as hay fever, affects over 400 million people worldwide. Triggered by airborne allergens like pollen, dust mites, or animal dander, it causes symptoms ranging from sneezing and itchy eyes to severe breathing difficulties. In the UK alone, one in four adults and one in eight children suffer from the condition, leading to at least 16 million doctor visits annually. Similar trends are seen in the U.S. and Australia.
Climate change is exacerbating the problem. Studies show rising pollen levels and longer allergy seasons, with symptoms becoming more severe. Left untreated, hay fever can lead to respiratory infections, asthma, and chronic upper airway diseases.
How immunotherapy works
Most allergy treatments, like antihistamines, only manage symptoms. Allergen immunotherapy (AIT), however, aims to retrain the immune system to tolerate allergens. The treatment involves gradual exposure to small doses of the allergen, either through injections or under-the-tongue drops or tablets.
"It's more of a cure," says Stephen Durham, emeritus professor of allergy and respiratory medicine at Imperial College London. "It may even prevent the progression from hay fever to asthma."
Yet access remains limited. Many patients are prescribed antihistamines instead of being referred to specialists for immunotherapy. "Hay fever is often trivialized by those who don't have it," Durham notes. "But it seriously impacts work, sleep, and quality of life."
Safety and effectiveness
Traditional allergy shots, while effective, carry a rare but serious risk of anaphylaxis-a severe allergic reaction to the treatment itself. In the UK, 26 deaths linked to subcutaneous immunotherapy were recorded between 1957 and 1986. Today, the risk is lower, but patients must still wait 30 minutes after each injection for observation.
Sublingual immunotherapy offers a safer alternative. Trials show it has a much lower risk of anaphylaxis, with no reported fatalities. Common side effects include temporary tongue itching or swelling. The World Health Organization endorsed the method in 1998, legitimizing it as a global treatment option.
However, adherence is key. Patients must take daily tablets or drops for 8 to 16 weeks before pollen season begins, continuing for three years to achieve long-term remission. In one trial, patients on sublingual immunotherapy reported severe symptoms on just 6% of days during allergy season, compared to 16% for those on a placebo.
Limitations and alternatives
Despite its promise, sublingual immunotherapy is not universally available. The U.S. Food and Drug Administration has approved it only for dust mites, ragweed, and grass pollen. "Many of my patients are allergic to tree pollen," says Barrie Cohen, a pediatric allergist in New Jersey. "I can't help them with an FDA-approved product."
For patients with severe asthma or those who don't respond to immunotherapy, biologics-medications that target immune pathways-offer another option. These can cost up to £20,000 ($25,000) per year, compared to less than £1,000 ($1,300) for immunotherapy.
For most patients, a combination of nasal sprays (containing antihistamines and corticosteroids) and trigger reduction-like keeping windows closed and showering after outdoor exposure-can provide relief. "The most effective treatment is a spray with both antihistamine and corticosteroid," Scadding says. "But it must be used regularly, even on symptom-free days."
A growing toolkit
Research continues to expand the options for allergy sufferers. A study of over 45,000 immunotherapy patients found they had fewer asthma-related prescriptions and were less likely to develop pneumonia compared to those who didn't receive the treatment. Another trial showed children on sublingual immunotherapy were 29% less likely to develop asthma symptoms.
"We have very effective treatments for the majority of patients," Durham says. "The message is clear: hay fever is not trivial, and proper treatment can transform lives."
