Environmental allergies are an enormously common but often poorly-managed condition. The standard playbook — a daily nasal steroid, a non-drowsy antihistamine, eye drops in season — is genuinely effective for many patients. But for a meaningful minority, no combination of these medications brings their symptoms under control. For that group, allergy immunotherapy is one of the few interventions in modern medicine that actually modifies the underlying disease.
What "environmental allergies" actually means
The umbrella covers several related diagnoses driven by the same IgE-mediated mechanism: allergic rhinitis (hay fever), allergic conjunctivitis, allergic asthma, and a subset of atopic dermatitis. The triggers are predictable: tree pollen in early spring, grass in late spring through mid-summer, ragweed and other weeds in late summer through fall, and the year-round culprits — house dust mite, animal dander (cat, dog), cockroach in some urban environments, and mould spores.
Why medications alone often aren't enough
Daily intranasal corticosteroids (fluticasone, mometasone, budesonide) and second-generation oral antihistamines (cetirizine, loratadine, fexofenadine, bilastine) remain the first-line treatment and they work for many people. Adjuncts — ophthalmic mast-cell stabilisers, leukotriene receptor antagonists, saline rinses — can be layered as needed.
The challenge is that all of these treatments are symptom-suppressing. They do nothing to the immune system's underlying sensitisation. When the medication stops, the symptoms return immediately. Many patients reasonably ask whether something else can be done.
How allergy immunotherapy works
Allergen-specific immunotherapy works by exposing the immune system to small, gradually increasing doses of the allergen over time. The mechanism involves a shift away from the Th2-dominant, IgE-producing response toward regulatory T-cell activity and IgG4 production. In practical terms: the immune system stops treating pollen, dust mite, or animal dander as a threat.
There are two main delivery routes in Canadian practice:
- Subcutaneous immunotherapy (SCIT) — "allergy shots." Administered in a physician's office. Can be customised to cover multiple allergens at once.
- Sublingual immunotherapy (SLIT) — daily tablets dissolved under the tongue. First dose taken in clinic under observation; subsequent doses at home.
SCIT — the long-established option
SCIT has the longest track record (decades of use) and is the route of choice when a patient has multiple allergies that need simultaneous coverage. Typical structure:
- Build-up phase: weekly injections in clinic, with the dose escalating each visit, for roughly 3 to 6 months.
- Maintenance phase: a fixed maintenance dose every 4 weeks for 3 to 5 years.
Most patients begin to notice meaningful symptom improvement within 6 to 12 months. The therapy is continued for several years because the goal is durable benefit — many patients enjoy years to decades of remission after completing a full course.
SLIT — the at-home option
Sublingual tablets are currently approved in Canada for ragweed, grass, dust mite, and tree pollen. They are taken once daily at home after an observed first dose. They are well-suited to single-allergen patients who prefer not to attend frequent clinic appointments, and to children who tolerate them well. SLIT is generally continued for 3 years to produce durable benefit.
Who is a candidate?
Immunotherapy is most often considered for:
- Patients with moderate-to-severe seasonal or perennial allergic rhinitis whose symptoms persist on standard medications
- Patients with allergic asthma triggered by a documented environmental allergen
- Patients who want to reduce long-term medication burden
- Patients with a clearly defined allergen on testing whose exposure pattern matches their symptoms
Skin-prick testing or serum-specific IgE is performed before starting therapy to confirm sensitisation and identify the right targets.
What to realistically expect
Immunotherapy is a commitment — 3 to 5 years for SCIT, 3 years for SLIT — but the outcome data are strong. The majority of patients experience significant, durable improvement that often persists for many years after stopping treatment. It is one of the rare therapies in chronic care that can plausibly be described as treating the disease rather than managing it.
If your current allergy regimen isn't working, or if you would prefer not to rely on daily medication for the rest of your life, a specialist consultation is the right next step. Our Allergy Rapid Access Clinic sees most referred patients within the same week.