Why some people have allergies and others do not

The short answer to why some people have allergies while others don’t is a mixture of inherited susceptibility, immune-system history and the environment a person lives in. An allergy is not a sign of personal weakness or simply a “strong” immune system. It is a specific immune response to a substance that is usually harmless, such as pollen, mould spores, dust mites, foods or insect venom.

Sensitisation can occur when the immune system first encounters an allergen, although the route, dose, timing and any existing inflammation influence the outcome. After sensitisation, later contact may cause sneezing, swelling, hives, wheezing or a severe systemic reaction. Some people become sensitised without symptoms, while others react to an amount that a tolerant person barely notices.

Allergy is a specific immune response

Allergy begins when immune cells identify a particular substance as a threat. For common immediate allergies, B cells produce immunoglobulin E, or IgE, which attaches to mast cells and other immune cells. When the allergen returns, it can trigger those cells to release histamine and other inflammatory chemicals.

The resulting symptoms depend on where exposure occurs. A nasal reaction may produce congestion and sneezing, skin contact may lead to itching and hives, and a systemic reaction may affect breathing, circulation or both. Insect venom, some medicines and latex can also cause serious reactions in susceptible people.

Not every immune reaction is IgE-mediated. Some allergies involve delayed T-cell activity, while conditions such as coeliac disease are immune-mediated but not conventional IgE allergies. A food intolerance is different again: lactose intolerance, for example, reflects difficulty digesting a sugar rather than an allergen-specific immune attack.

Genes and life experience shape susceptibility

Susceptibility is partly written into genetics. Variants in genes controlling skin barriers, immune recognition and regulatory pathways can increase the likelihood of sensitisation. A family history of eczema, asthma or food allergy often signals higher risk, yet these conditions are polygenic: many small effects combine with environment, so inheritance predicts tendency more reliably than outcome.

Life experience then changes the immune response. Repeated exposure through the nose, skin or gut can help establish sensitisation, while the timing of exposure in infancy may matter. Antibiotics, diet, infection, pollution, stress and the household microbiome are all being studied, but no single factor explains national or family patterns. The old idea that fewer childhood infections automatically prevent allergy is too simple.

This interaction helps explain why one sibling reacts to grass pollen while another does not. It also explains why the same person may tolerate a food in one setting and react in another. Public discussions of habit, environment and decision-making, including ideas on human behaviour, provide useful context for this meeting of biology and daily life.

Australian seasons create different allergy profiles

Australia’s climatic range means there is no single national allergy calendar. Southern states often have a pronounced spring pollen period, while tropical Queensland has different mould, mite and vegetation patterns. Australians commonly call the spring flare-up the “sniffly season”, although that phrase covers several conditions rather than one illness.

Melbourne is well known for a strong spring grass-pollen season, especially when warm, dry and windy conditions follow winter rain. Sydney also has a recognisable spring pattern, with plane-tree pollen joining grass and other airborne allergens. Pollen counts can change quickly with weather, so a neighbourhood routine that works in one week may fail in the next.

Brisbane’s warm, humid environment creates different pressures. Outdoor mould spores can rise in damp weather, and dust mites thrive in bedding and carpets; indoor damp can add another problem if leaks or poor ventilation are left unattended. Along the coast and in the tropics, year-round mite exposure may matter more than a short, intense pollen season.

Rain usually suppresses airborne pollen, but wet conditions can encourage mould. Bushfire smoke is mainly an airway irritant rather than an allergen, yet it can aggravate asthma and rhinitis. Melbourne’s familiar thunderstorm asthma illustrates another interaction: heat, humidity, pollen fragments and other airborne particles can place extra strain on lungs during a storm.

The same label can hide different triggers

In Australian usage, “hay fever” usually means allergic rhinitis, although it can include symptoms caused by grass or tree pollen, mould spores, animal dander or dust mites. These triggers may produce almost identical sneezing, congestion and itchy eyes. The label describes the symptoms; it does not identify what is causing them, which matters for selecting treatment.

Food allergy creates a different set of risks. Food Standards Australia New Zealand rules require clear declarations for major allergens such as milk, egg, peanut, soy, tree nuts, fish, shellfish, cereals containing gluten and sesame. Statements such as “may contain” warn about cross-contact rather than deliberate inclusion, yet many consumers still need to read the full label because manufacturing conditions can change.

Cross-reactivity adds another layer. A person sensitised to certain pollens may also react to raw apple, pear, carrot, celery or melon, and cooking can change the reaction. Some apparent food allergies are caused by this cross-reactivity rather than a separate allergy to that food. A history of reactions, the food’s form and the timing all help clinicians separate the possibilities.

Tests need clinical context to be useful

Skin-prick testing and blood tests for specific IgE can identify sensitisation, but they do not diagnose symptoms on their own. A positive result means the immune system recognises something; it may not mean the person will react at every exposure, and some results reflect harmless sensitisation. Test choice also depends on the suspected trigger and the history.

For food allergy, a medically supervised oral food challenge is often the most reliable way to establish a reaction, while component testing can help distinguish true allergy from pollen cross-reactivity. No home challenge is safe when a previous reaction involved hives, breathing trouble, faintness or vomiting. A clinician should interpret all results alongside exposure patterns and examination findings.

In Australia, many people begin with a GP through Medicare and then ask about referral to an allergist or clinical immunologist. Specialists may work in private practice, and not every test or treatment receives the same subsidy. Symptoms that repeatedly disrupt sleep, school, work or exercise merit review, while wheezing and breathlessness require attention to asthma rather than treatment with an antihistamine alone.

Reducing exposure while protecting everyday life

Reducing exposure starts with matching the strategy to the trigger. During high pollen counts, people can limit time outdoors in the morning, keep windows closed when winds are strong, shower and change clothes after outdoor activity, and use a vacuum cleaner with a suitable fine-particle filter. A pharmacist or doctor can help select antihistamines or corticosteroid nasal sprays for suitable people.

Homes need different measures. Hot-washing bedding, reducing indoor humidity where practical, using mattress and pillow covers, and repairing leaks can limit mites and mould. Immunotherapy for dust mites may suit selected people with troublesome rhinitis or asthma, but it requires assessment and regular administration. It does not suit every allergy and is not a guaranteed cure.

Food reactions require strict label checking, care with cross-contact and an individual emergency plan. Anyone prescribed an adrenaline autoinjector should carry it, know the signs that it is needed and practise the steps instructed by their clinician. Injected adrenaline is not a substitute for emergency care, and a person with breathing difficulty, throat swelling or collapse needs urgent assistance.

Treatment can require repeated appointments, testing and long-term medication, so cost deserves attention. When comparing clinic fees, private cover and expenses that may not be reimbursed, personal finance guidance can help households make a sustainable plan rather than commit under pressure. Effective control should also improve sleep, concentration, exercise and social participation.

AtsMotorSports places this explanation within its broader remit of making finance, politics, healthcare and general-interest subjects understandable; the publication background appears in about AtsMotorSports. Clear examples and practical context can make a medically complex subject easier to recognise without pretending that one routine fits every person.

Take action now by recording symptoms, locations, weather, foods and medicines for two weeks, checking Australian pollen forecasts and arranging a GP review if symptoms persist or interfere with daily life. Follow the written asthma and emergency plans provided by your clinician, carry prescribed adrenaline, and call 000 for a rapidly worsening reaction, breathing difficulty, throat swelling or collapse.