An allergy is the immune system reacting to something harmless to most people. It takes four main forms: food, environmental, drug and insect sting. That can mean a blocked nose and itchy eyes, hives, or a reaction needing emergency care.
An allergy is not an intolerance. Lactose intolerance involves digestion, not the immune system, and does not cause anaphylaxis. Health Canada research shows the gap: 9.3 percent of Canadians self-reported a food allergy in the 2016 national survey, while 6.1 percent had a probable food allergy.
A positive test alone is also not an allergy. Allergists read results against what happens on exposure, because sensitisation can show without causing symptoms.
The last two point to anaphylaxis, an emergency covered below.

Some risk factors cannot be changed:
Others can often be worked on, usually with support from a health care team:
Assessment starts with the history: what happened, how soon after exposure, and whether it has happened before. Testing is read against that. An allergist confirms an airborne or food allergy with a skin prick test, where allergen extract is placed on the skin and lightly pricked, or a blood test for allergen-specific IgE. A supervised oral food challenge settles uncertain food cases. Drug allergy is assessed similarly, sometimes to confirm or remove a label such as penicillin allergy carried for years.
Care combines avoiding a confirmed trigger, treating symptoms, and readiness for a severe reaction:
These are decisions for you and your own clinician.
Nothing available makes an allergy go away for good. Allergen immunotherapy comes closest, and the CSACI manual describes courses running three to five years, so it is neither quick nor suitable for everyone. Research is aimed at shorter, more targeted approaches: peptide and recombinant allergen preparations, and biologic medicines that block IgE and type 2 inflammation. Food allergy studies are testing oral immunotherapy.
Taking part is voluntary, informed consent comes first, you can stop at any time without affecting your regular care, and no one can say in advance whether a study will help you.
This page is written in plain language for people considering clinical research. It is general health information, not medical advice, and it does not replace a conversation with your own doctor or nurse practitioner.
An allergy involves the immune system reacting to a substance, and it can affect the skin, the nose and eyes, the airways, the gut and the circulation at once. An intolerance, such as lactose intolerance, involves digestion rather than the immune system, is usually limited to the gut, and does not cause anaphylaxis. The distinction matters for how a reaction is treated and for whether you need to carry epinephrine. Health Canada research found many more Canadians report a food allergy than have a reaction fitting an allergic pattern, which is one reason allergist assessment is useful.
Yes. The Canadian Society of Allergy and Clinical Immunology's anaphylaxis emergency plan directs that after epinephrine is given, you call 9-1-1 and go to the nearest hospital immediately, ideally by ambulance, because the reaction can worsen or come back. The plan also states that a second dose can be given as soon as five minutes after the first if symptoms have not improved, and advises staying near a hospital or within reach of emergency services for 48 hours afterwards.
Because avoidance is not always possible and current treatments do not suit everyone. Allergen immunotherapy takes three to five years, and daily medicines control symptoms without changing the allergy. Studies are testing shorter immunotherapy schedules, biologic medicines that block allergic pathways, and oral immunotherapy for food allergy. Seasonal allergy studies are timed around the pollen calendar, so recruitment often happens months before the season starts. Taking part is voluntary, you give informed consent first, and you can withdraw at any time without affecting your regular care.