A new generation of treatments is renewing hopes that seasonal allergies could one day be controlled at their source, rather than simply managed through symptoms.

Researchers and clinicians are revisiting allergen immunotherapy, an approach designed to retrain the immune system. The idea is straightforward: gradually expose the body to allergens so it becomes less reactive over time.

Glenis Scadding recalls one of her earliest patients treated with sublingual immunotherapy four decades ago. The man’s hay fever was so severe that even walking to a nearby train station triggered wheezing. Her method involved administering small doses of birch pollen extract under the tongue to build tolerance.

"He turned up at my house with a case of wine, because I had completely altered his life in the spring," says Scadding, vice president of the non-profit Euforea and honorary consultant allergist and rhinologist at University College Hospital London, UK.

"And then I got so much flack, I stopped."

Allergic rhinitis affects more than 400 million people globally. The condition occurs when the immune system overreacts to harmless airborne substances such as pollen, dust mites or animal dander. Symptoms range from sneezing and itchy eyes to congestion and, in severe cases, breathing problems. When triggered by seasonal pollen, it is commonly known as hay fever.

Beyond immediate discomfort, the condition can have lasting health effects. It is associated with an increased likelihood of respiratory infections and can contribute to the development of asthma. In the UK alone, about one in four adults and one in eight children are affected, generating millions of medical visits annually. Similar prevalence has been reported in the United States and Australia, with evidence suggesting rates are rising and symptoms worsening, partly due to climate change.

Specialists say treatment options have improved significantly. While most therapies focus on symptom relief, allergen immunotherapy (AIT) aims to modify the disease itself by reducing the body’s sensitivity to allergens. It may also interrupt the progression from hay fever to asthma.

Despite its potential, access remains limited. "Very few people get to see the right person to treat their disease – and they don't get to see them at the stage when the disease is early, uncomplicated and easy to treat," says Scadding.

Experts argue that allergic rhinitis is frequently underestimated, even within the medical community. Stephen Durham, emeritus professor of allergy and respiratory medicine at Imperial College London and Royal Brompton Hospital, says patients are often advised to rely on over-the-counter antihistamines rather than being referred for specialist care or long-term treatment strategies.

"Hay fever is a major problem, and it's often trivialised by those who don't have it," Durham says. "If you think about what we do in life, we work, we sleep, and we have fun. And all of those things are seriously impacted by hay fever."

The condition can disrupt sleep, increase fatigue and impair concentration. In children, it has been linked to reduced academic performance. Chronic inflammation of the airways also leaves sufferers more vulnerable to infections, sometimes doubling their frequency. Left untreated, it may lead to persistent upper airway disease or ear complications.

The relationship between hay fever and asthma is particularly concerning. "There's a concept of 'one airway, one disease'," says Barrie Cohen, a paediatric allergist in New Jersey and author of a 2023 American Academy of Pediatrics review on allergic rhinitis. She explains that inflammation in the upper airways can extend to the lower respiratory tract through shared immune pathways, increasing asthma risk.

Although cases are rising, hay fever itself is not new. In 1828, London physician John Bostock documented seasonal symptoms based on his own experience and those of 28 patients, describing congestion, sneezing and watery eyes.

Efforts to treat the condition through immunotherapy date back more than a century. In 1911, researchers found that injecting patients with grass pollen extracts could reduce symptoms in subsequent seasons. By the 1950s, controlled trials confirmed its effectiveness, and by the 1980s, allergy shots had become a standard treatment.

However, safety concerns emerged. "Injection immunotherapy has occasionally killed people," says Scadding, referring to rare cases of anaphylaxis. Though such reactions occur in roughly one per 2 to 2.5 million injections and are now even less common due to improved protocols, earlier incidents led to stricter regulations. In the UK, patients were once required to remain under observation for two hours after injections, making the treatment logistically challenging.

These limitations fueled interest in oral alternatives. Sublingual immunotherapy, which delivers allergens under the tongue, gained attention despite early skepticism.

"Sublingual was regarded as a real 'fringe' thing which wasn't going to work," Scadding says. "So I stopped doing it for a while."

Subsequent studies demonstrated that the method significantly reduces the risk of severe reactions while maintaining effectiveness. "There have been no fatalities. Serious adverse events are very rare," Scadding says, noting that mild local reactions such as itching or swelling are more common.

The World Health Organization formally recognized sublingual immunotherapy as a viable option in 1998, helping to expand its global acceptance.

Adherence remains a key challenge. Treatment typically involves taking a daily tablet or drops under the tongue for several weeks before pollen season begins. Starting 16 weeks in advance can control symptoms in about 85% of patients, according to Durham.

For lasting benefits, patients are advised to continue therapy for three years. "If you treat people for three years, you can induce long-term disease remission," Durham says. Clinical trials have shown substantial reductions in symptom days among those receiving active treatment compared with placebo.

Evidence also suggests that improvements persist after treatment ends. Some studies report continued symptom relief for up to two years post-therapy.

Still, availability is limited. In the United States, approved sublingual treatments target only a handful of allergens, including dust mites, ragweed and grass pollen. "A lot of my patients have tree pollen allergy – I can't really help them if I want to use an on-label, FDA-approved product," says Cohen, who often turns to injection therapy in such cases.

Large-scale studies indicate that immunotherapy reduces reliance on medications for both hay fever and asthma and lowers the risk of complications such as pneumonia. It may also help prevent asthma from developing in children. In one trial, children receiving sublingual treatment were significantly less likely to develop asthma symptoms than those given a placebo.

However, not all patients are candidates. Those with severe or poorly controlled asthma may face higher risks, even though serious reactions remain rare. For these individuals, biologic drugs that target specific immune pathways offer an alternative, sometimes used alongside immunotherapy.

While effective, biologics are costly and do not provide the same long-term remission. "But they don't induce long-term disease remission like immunotherapy," Durham says. "And they cost between £12-20,000 a year while, for example, the immunotherapy that we've been talking about – those tablets cost less than £1,000 ($1,300) a year."

For many patients, cost and treatment duration remain significant barriers. As a result, symptom-based therapies continue to play a central role.

"The single most effective treatment that we have that patients can easily access is a spray which has antihistamine as well as corticosteroid in it," Scadding says, noting that combination nasal sprays outperform single-drug options.

Durham emphasizes the importance of timing and consistency. Starting treatment before allergy season and maintaining daily use can both relieve and prevent symptoms.

Proper technique is also critical. Oral antihistamines, while widely used, are generally less effective because they do not act directly on nasal tissues. Newer, second-generation options such as cetirizine or loratadine are preferred due to their reduced sedative effects, as older versions have been linked to increased accident risk.

Reducing exposure to allergens can further ease symptoms. Experts recommend keeping windows closed, using air purifiers and wearing protective gear like sunglasses or masks outdoors. Hygiene measures, including washing exposed skin and showering before bed, can help limit pollen exposure.

"If you're sleeping in that pollen on the pillowcase, you can imagine it's not good to breathe in," Cohen says.

Even with these strategies, complete avoidance is often impractical. Outdoor activities remain an important part of daily life, particularly in warmer months.

Still, specialists stress that effective treatments are widely available. "We've got very effective treatments for the majority of patients," Durham says. "The message is that it's trivialised, and people don't understand how to treat it properly."