What is allergy desensitisation?
Desensitisation — allergen immunotherapy — gives the immune system controlled, repeated exposure to the exact thing it overreacts to, in doses that climb slowly enough to be safe. Over months, the response shifts from alarm to tolerance.
What actually changes
Allergy is an IgE-driven mistake: a harmless protein is treated as a threat, and mast cells release histamine within minutes of contact. Immunotherapy redirects that response — blocking IgG4 antibodies rise, regulatory T cells expand, and mast cells and basophils become harder to trigger. The result is fewer symptoms on the same exposure, and less need for rescue medication.
It is the only allergy treatment with a benefit that persists after the course ends, and the only one shown to reduce the chance of new sensitisations and of asthma developing in allergic children.
Subcutaneous immunotherapy (SCIT)
An allergen extract injected into the fat under the upper arm, in a clinic equipped to treat anaphylaxis. Doses rise weekly through a build-up phase, then hold at a maintenance dose given every four to eight weeks for three to five years.
- Best established route for grass, tree, weed, house dust mite, mould and animal allergy.
- The only route with proven benefit for bee and wasp venom allergy, where it is close to fully protective.
- Requires a 30-minute wait after each injection, and adrenaline on the premises.
Sublingual immunotherapy (SLIT)
Drops or a fast-dissolving tablet held under the tongue, taken daily at home. The first dose is given under supervision; the rest is self-administered.
- No injections, no weekly clinic visits — which matters most for children and for patients far from a specialist.
- Side effects are usually local: itching or tingling in the mouth for the first week or two.
- Systemic reactions are rare, but adherence has to be genuine — a course only works if it is taken daily.
Oral immunotherapy for food allergy (OIT)
Measured amounts of the food itself — peanut, egg, milk, cashew — eaten daily, increased in graded steps under specialist supervision. The aim is to raise the reaction threshold so that an accidental exposure stops being dangerous.
- Protection is dose-dependent and generally requires ongoing daily intake to be maintained.
- Reactions during up-dosing are common; this is a supervised programme, never a home experiment.
- Sublingual immunotherapy for food allergy uses much smaller doses, with a gentler side-effect profile and a lower ceiling of protection.
Is it for you?
Immunotherapy suits people whose symptoms are driven by a confirmed allergen, who have tried avoidance and medication and still have a problem worth three to five years of treatment. It is not started during uncontrolled asthma, and it needs a proper diagnostic work-up first — a positive test on its own is not a reason to treat.