The only treatment that changes the allergy rather than masking it.
You are given a very small, measured dose of what you react to, increased in steps, until your immune system stops treating it as a threat. It is slow, it is a course of years, and for the right patient it is the only thing that leaves you better after you stop.
The short version
- Almost every allergy medicine relieves the symptom. Immunotherapy is the one treatment that tries to change the allergy itself.
- It works by giving tiny, slowly increasing doses of the exact thing you react to, until your immune system stops treating it as a threat.
- It is a three-year course, taken daily as drops under the tongue or as injections at the clinic. Stopping early wastes it.
- It suits some people and not others. You will be told plainly if it is not right for you.
What it is
Allergen immunotherapy — also called allergy immunotherapy, or simply desensitisation — has been in clinical use for over a century. The principle is simple: repeated, controlled exposure to a precisely measured amount of an allergen teaches the immune system tolerance, in the same way it is tolerant of everything else you breathe in every day.
The useful way to think about it is training, not medication. An antihistamine is a mute button: it silences the alarm while the drug is in your system, and the alarm returns when it wears off. Immunotherapy is closer to teaching the alarm that the postman is not a burglar.
How we choose the route
Two delivery routes are in clinical use. For most patients with allergic rhinitis or allergic asthma in India, sublingual drops are the practical choice — and it is honest to say that convenience is part of why.
| Sublingual — drops or tablets (SLIT) | Injections (SCIT) | |
|---|---|---|
| How it is taken | Under the tongue, held two minutes, at home. About as much of your morning as brushing your teeth. | An injection at the clinic, followed by 30 minutes of observation before you leave. |
| Clinic visits | Review every 2–3 months. | Weekly through build-up, then roughly monthly. |
| Build-up phase | Dose escalated over about four weeks. | Four to six months of weekly injections to reach maintenance. |
| Common side effects | Itchy mouth, tingling lips, mild throat irritation in the first fortnight. Usually settles. | Redness, swelling and itching at the injection site are expected. |
| Serious reactions | Rare. | Uncommon — and the reason injections are given only where a reaction can be treated immediately. |
| Best suited to | Children, needle-averse adults, anyone who cannot travel to the clinic weekly. | Selected patients, including some single-allergen and venom cases. |
What three years actually looks like
- Weeks 1–4
Build-up
The dose is increased in steps under supervision. Mild mouth or lip itching is common and settles. This is the phase people mistake for a reaction.
- Months 3–6
The first honest sign of change
Most patients notice fewer bad days and less reaching for rescue medicine. Not weeks — months. Anyone promising relief in a fortnight is overselling.
- Year 1–2
Maintenance
A steady daily dose with review every three months. Many patients reduce or stop their daily antihistamine during this period.
- Year 3
Course complete
Treatment is stopped. The benefit is intended to persist afterwards — which is the entire point of having done it.
The question nobody answers
What if I stop early?
Benefit accrues with cumulative dose. Stopping during build-up means you have taken the inconvenience and the small risk without banking anything durable. Stopping at a year usually means symptoms return much as before.
Abandoning immunotherapy at eighteen months tends to waste the eighteen months. That is not a threat — it is the reason I would rather spend the first consultation making sure you actually want to do this than start you on something you will drop in month seven. If your circumstances change mid-course, come and talk about it rather than simply stopping.
Side effects, told straight
Three tiers
Common, local, short-lived
With drops: itching of the mouth, tingling lips, mild throat irritation, occasionally ear itching — typically in the first two weeks, easing as the body adjusts. With injections: redness, swelling and itching at the site, settling within hours.
Less common, systemic, mild
Sneezing, nasal congestion or hives after a dose. In people with asthma, a temporary increase in chest symptoms. Report these — they usually mean the dose needs adjusting, not stopping.
Rare, serious
A generalised allergic reaction — difficulty breathing, swelling of the throat or tongue, faintness. This is rare, and it is why injections are given only in a clinic with resuscitation drugs and equipment immediately to hand, and why you wait thirty minutes afterwards. Risk is highest during build-up and falls substantially once you are on maintenance.
Call 108, or go to the nearest emergency department, if you have:
- Difficulty breathing, wheezing you cannot control, or a feeling of choking
- Swelling of the lips, tongue or throat, or a tight throat and difficulty swallowing
- A widespread rash together with faintness, dizziness or collapse
- Sudden severe symptoms after a food, a sting, a medicine or an immunotherapy dose
If you have been prescribed an adrenaline auto-injector, use it first and then go. Do not wait for a clinic appointment.
Candidacy
Immunotherapy is not right for everyone
It works best for allergic rhinitis, allergic conjunctivitis and allergic asthma driven by a small number of clearly identified allergens — house dust mite, specific pollens, moulds, cat or dog — and for venom allergy. It works less well when the list of triggers is very long, when the diagnosis is not really allergy, or when doses are missed for weeks at a time.
It is generally not started where there is uncontrolled or severe asthma, significant cardiovascular disease, active autoimmune disease, or during pregnancy — although an established course may often be continued through a pregnancy. Beta-blockers need discussion before starting. And it needs a patient who can commit to the schedule.
Selection is doing most of the work here, and selection is what the first consultation is for.
Evidence
What the guidelines actually say
Allergen immunotherapy is recommended in the major international allergy guidelines — ARIA for allergic rhinitis, the EAACI allergen immunotherapy guidelines, and World Allergy Organization position papers. What they establish is that it is the only available treatment that modifies the underlying allergic disease rather than suppressing its symptoms, and that in appropriately selected patients the benefit persists after the course ends.
What they also make clear, and what commercial sites tend to leave out: the strength of the recommendation varies by allergen and by product, the quality of evidence is better for some indications than others, and standardisation of extracts matters. Those caveats are part of an honest conversation, and you will get them here rather than a single number designed to close a sale.
Before you start
Will this work for me?
For properly selected patients with a small number of identified allergens, it works well in the majority. It works poorly when the diagnosis is uncertain or when doses are missed. That is why the testing and the consultation come first — and why some people are told immunotherapy is not the right answer for them.
What if I miss doses?
A missed day is not a problem — take the next dose as usual. More than about a week off and the dose usually has to be stepped back down, which costs you time rather than progress. If you know a trip, a surgery or an illness is coming, message the clinic first and you will be told what to do.
Can my child have immunotherapy?
Yes, and there is a reasonable argument for starting earlier rather than later, since treating allergic rhinitis in childhood may reduce the chance of asthma developing. Sublingual drops are generally preferred in children precisely because there are no needles. The child needs to be old enough to report symptoms reliably.
What if it doesn't work?
You will know by around the six-month review, and that review exists for exactly this decision. If there has been no meaningful change and dosing has been consistent, we stop rather than spend two more years on it. That conversation is part of the treatment, not a failure of it.
Why not just keep taking the tablet?
Because it is doing a different job. That is a perfectly reasonable choice if your symptoms are mild and well controlled. It becomes a poor one when you have been taking it every day for years, at a rising dose, and are still planning your life around a season.
Immunotherapy asks a lot of a patient — three years of daily doses for a benefit that arrives quietly, months in. I would rather talk someone out of starting than watch them stop halfway. If you begin it here, you will know exactly what you are agreeing to.