What are the main causes of allergy


A reaction produced by the body’s immune system when exposed to a normally harmless substance.

What is the impact?

About 20 per cent of the general population suffers from rhinitis. Of these people, about one third develops problems before the age of 10.

The overall burden of allergic rhinitis is better understood when you consider that 50 per cent of patients experience symptoms for more than four months per year and that 20 per cent own symptoms for at least nine months per year.

Those affected by hay fever suffer more frequent and prolonged sinus infection, and for those who also own red, itchy eyes, there is the risk of developing infective conjunctivitis due to frequent rubbing.

Persistent symptoms and poor quality sleep can result in lethargy, poor concentration and behavioural changes and impact on learning in young children.
Allergic rhinitis may predispose people to obstructive sleep apnoea, due to the upper airways collapsing during sleep.

This results in reduced airflow, a drop in oxygen levels and disturbed sleep.

Patients with allergic rhinitis also suffer from more frequent and prolonged respiratory infections, and asthma has been shown to be more hard to control unless allergic rhinitis is also managed.


The exaggeration of the normal effects of a substance. For example, the caffeine in a cup of coffee may cause extreme symptoms, such as palpitations and trembling.

What is the link between allergic rhinitis and asthma?

Allergic rhinitis has been found to be an extremely common trigger for asthma in both children and adults.

Allergic rhinitis can also exacerbate asthma, and it can make the diagnosis of asthma more difficult.

Around 80 per cent of people with asthma suffer from allergic rhinitis, and around one in four with allergic rhinitis has asthma.

There is now extremely excellent evidence to support the thought that asthmatics who glance after their upper airways well need less asthma medication and fewer hospital or GP visits.

When treating both asthma and allergic rhinitis, the first step is to discover out the cause of your problem. Once the causes own been identified, management regimes can be put into put to minimise the impact of the allergy, and this then reduces the need for medication.

What causes allergic rhinitis?

The most common triggers for people with allergic rhinitis are pollen, dust mite, pet and mould allergens.

Seasonal allergic rhinitis (hay fever) is generally triggered by wind-borne pollen from trees, grass and weeds.

Early spring symptoms point to tree pollen, while nasal allergy in tardy spring and summer indicates that grass and weed pollens are the culprits. And overlapping the grass season is the weed pollen season, which generally starts in tardy spring and extends through to the finish of summer.

In New Zealand the seasons are not extremely distinct and they vary throughout the country because of the diverse climates.

The season starts about one month earlier at the top of the North Island than the bottom of the South Island. Thus the hay fever season is not extremely well defined.

Allergic rhinitis that persists year-round (perennial allergic rhinitis) is generally caused by home dust mites, pets, or mould. People with allergic rhinitis are often allergic to more than one allergen, such as dust mite and pollen, so may suffer from symptoms for months on finish or every year round.

Irritants such as strong perfumes and tobacco smoke can aggravate this condition.

Foods do not frolic as large a role as had been thought in the past.


Where a substance causes unpleasant symptoms, such as diarrhoea, but does not involve the immune system.

People with an intolerance to certain foods can typically eat a little quantity without having any problems.

Sheet final reviewed: 22 November 2018
Next review due: 22 November 2021

What is allergic rhinitis?

Hay fever is the common name to describe allergic rhinitis and involves a recurrent runny, stuffy, itchy nose, and frequent sneezing. It can also affect your eyes, sinuses, throat and ears.

Love any other allergy, allergic rhinitis is an inappropriate immune system response to an allergen – most commonly home dust mite, pet, pollen and mould.

The allergen comes into contact with the sensitive, moist lining in your nose and sinuses and sets off the allergic response.

Hay fever is often considered a nuisance rather than a major disease and most people will self-treat. However, recent studies own revealed that hay fever has a huge impact on quality of life.

How do you diagnose allergic rhinitis?

Your doctor will confirm the specific allergens causing your rhinitis by taking a finish symptom history, doing a physical examination, and performing skin prick tests.

When does allergic rhinitis develop?

Allergic rhinitis typically develops in childhood.

What are the main causes of allergy

It is part of what we call the Allergic March, where children first develop eczema in infancy, sometimes followed by food allergy, and then go on to develop allergic rhinitis and then asthma.

The onset of dust mite allergy occurs often by the age of two, with grass pollen allergy beginning around three to four years of age. Tree pollen allergy develops from about seven years of age.

It is not unusual to develop hay fever during adulthood. It can take as few as two to three seasons to become sensitised to pollen, but it depends on the individual.

What are the symptoms?

Symptoms of allergic rhinitis can be any combination of itching in the back of the throat, eyes or nose, sneezing, runny eyes or nose, and blocked nose.

A person may own any or every of the following:

  1. stuffy nose every the time or during specific seasons
  2. breathing through the mouth
  3. reddened, pebbly lining in the lower eyelids
  4. rabbit-like movements of the nose
  5. snoring
  6. watery discharge from the nose every the time, occasionally or during certain seasons of the year
  7. headaches because of pressure from inside the nose
  8. frequent earaches, fullness in the ear, ear infections or hearing loss
  9. bouts of sneezing, especially in the morning
  10. repeated nosebleeds
  11. frequent throat-clearing
  12. dizziness or nausea related to ear problems
  13. nasal voice because of blocked nasal passages
  14. a horizontal crease across the nose as a result of constant rubbing
  15. chronic freezing without much fever
  16. dark circles under the eyes as a result of pressure from blocked nasal passages on the little blood vessels.

    Also known as "allergic shiners".

How is allergic rhinitis treated?

It is useful to identify your triggers and attempt and avoid them. This can be difficult.

Pets: Make certain you hold it exterior and never let it in the bedroom.

What are the main causes of allergy

It is never simple trying to decide on a new home for a pet, but in some cases this might be the best option. Even after you own removed your pet from your home, the allergens remain in furnishings for endless periods afterwards and can cause symptoms. You will need to thoroughly clean your walls, floors and carpets to remove the allergen.

Dust mites: Home dust mite reduction measures include mite-proof covers for the mattress, duvet and pillows.

What are the main causes of allergy

Removing items that collect dust from the bedroom will assist. A excellent quality vacuum cleaner with HEPA filter for the exhaust air is essential to ensure that allergen is not disseminated in the atmosphere. Bedding should be washed frequently in water hotter than 55ºC. If you own soft toys, freeze them overnight and air in the sun.

Pollen: It is hard to avoid pollen, however you can avoid going exterior when pollen counts are high. The quantity of pollen in the air is highest:
• In the morning
• Outside
• On windy days
• After a thunderstorm

See our pollen calendar for more information.


Non-sedating antihistamine tablets or liquid are useful in alleviating some of the symptoms of rhinitis.

They are helpful in controlling sneezing, itching and a runny nose, but are ineffective in relieving nasal blockage.

What are the main causes of allergy

They can be used alone or in combination with other medications, such as nasal sprays.

Corticosteroid (anti-inflammatory) nasal sprays reduce the inflammation in the lining of the nose. They work best when used in a preventative manner, just love preventers for asthma. For example, they may be used for weeks or months at a time during an allergy season. Enquire your doctor about the appropriate medication for your condition.

Decongestant nasal sprays can be used to unblock the nose, but should not be used for more than a few days at a time. Prolonged use may result in worsening of the nasal congestion.

Eye drops: The eye problems that sometimes happen with allergic rhinitis may not always reply to the above medications.

Eye drops containing decongestants alone or in combination with antihistamine are available for mild to moderate eye problems.

What are the main causes of allergy

Eye irritation is one side effect. Prolonged use of decongestant eye drops can also cause rebound worsening when stopped. Some brands of eye drops can be used preventatively and are safe to use for prolonged periods — enquire your doctor for more specific information.

Saline washes may assist to clear your nose and soothe the lining of your nose. These are available from most pharmacies.

Desensitisation, or immunotherapy, is used to 'turn off' the abnormal response of the immune system to an allergen if medication does not work.

What are the main causes of allergy

It is mainly used to relieve the symptoms of hay fever and allergic asthma to pollen, mould, home dust mite and pet allergen, as well as to control severe reactions to insect stings.

To start, a extremely dilute dose of the substance you are allergic to is istered by injection once or twice a week. This dose is gradually built up over three to four months on average, until a maintenance dose is achieved. Shots are then given monthly for at least three years.

This method of treatment is the only one that deals with the underlying cause of allergic rhinitis.

Not everyone benefits from treatment, however the vast majority of patients show at least some degree of improvement. Enquire your allergy specialist about whether you are a excellent candidate for immunotherapy.

Sublingual immunotherapy is another method, where drops of the allergen solution are taken under the tongue. It is not widely used exterior of Europe.

This information is available as a fact sheet.

December 2008

This fact sheet is based on information available at the time of going to print but may be subject to change.

What are the main causes of allergy

It is significant to remember that we are every diverse and individual cases require individual medical attention. Please be guided by your GP or specialist.

Acknowledgments: We would love to Associate Professor Rohan Ameratunga, Clinical Immunologist, Auckland Hospital, for assistance in writing this information. This fact sheet is also based on information provided by the Australasian Society of Clinical Immunology and Allergy and the National Asthma Council Australia.

These substances are called allergens, and the most common are proteins in pollen from trees and grasses, food, fur, dust mites or mould, in addition to metals and substances used in cosmetics and pharmaceuticals.

An allergic reaction is an overreaction of the immune system to an allergen.

Allergy development takes put in two stages, with an initial sensitisation or induction phase followed by an effector phase (see figure below). Clinical symptoms of allergy only appear in the effector phase. Some people do not progress from the induction phase and will therefore not present clinical symptoms of allergy.

The figure shows the phases of allergy development

Common allergies

Substances that cause allergic reactions are called allergens.

The more common allergens include:

  1. grass and tree pollen – an allergy to these is known as hay fever (allergic rhinitis)
  2. animal dander, tiny flakes of skin or hair
  3. dust mites
  4. insect bites and stings
  5. food – particularly nuts, fruit, shellfish, eggs and cows’ milk
  6. medicines – including ibuprofen, aspirin and certain antibiotics
  7. mould – these can release little particles into the air that you can breathe in
  8. latex – used to make some gloves and condoms
  9. household chemicals – including those in detergents and hair dyes

Most of these allergens are generally harmless to people who are not allergic to them.

Getting assist for allergies

See a GP if you ponder you or your kid might own had an allergic reaction to something.

The symptoms of an allergic reaction can also be caused by other conditions.

What are the main causes of allergy

A GP can assist determine whether it’s likely you own an allergy.

If they ponder you might own a mild allergy, they can offer advice and treatment to assist manage the condition.

If your allergy is particularly severe or it’s not clear what you’re allergic to, they may refer you to an allergy specialist for testing and advice about treatment.

Find out more about allergy testing

Symptoms of an allergic reaction

Allergic reactions generally happen quickly within a few minutes of exposure to an allergen.

They can cause:

  1. sneezing
  2. a runny or blocked nose
  3. red, itchy, watery eyes
  4. wheezing and coughing
  5. a red, itchy rash
  6. worsening of asthma or eczema symptoms

Most allergic reactions are mild, but occasionally a severe reaction called anaphylaxis or anaphylactic shock can happen.

This is a medical emergency and needs urgent treatment.

What causes allergies?

Allergies occur when the body’s immune system reacts to a specific substance as though it’s harmful.

It’s not clear why this happens, but most people affected own a family history of allergies or own closely related conditions, such as asthma or eczema.

The number of people with allergies is increasing every year.

The reasons for this are not understood, but 1 of the main theories is it’s the result of living in a cleaner, germ-free environment, which reduces the number of germs our immune system has to deal with.

It’s thought this may cause it to overreact when it comes into contact with harmless substances.

How to manage an allergy

In many cases, the most effective way of managing an allergy is to avoid the allergen that causes the reaction whenever possible.

For example, if you own a food allergy, you should check a food’s ingredients list for allergens before eating it.

There are also several medicines available to help control symptoms of allergic reactions, including:

  1. antihistamines – these can be taken when you notice the symptoms of a reaction, or before being exposed to an allergen, to stop a reaction occurring
  2. decongestants – tablets, capsules, nasal sprays or liquids that can be used as a short-term treatment for a blocked nose
  3. lotions and creams, such as moisturising creams (emollients) – these can reduce skin redness and itchiness
  4. steroid medicines – sprays, drops, creams, inhalers and tablets that can assist reduce redness and swelling caused by an allergic reaction

For some people with extremely severe allergies, a treatment called immunotherapy may be recommended.

This involves being exposed to the allergen in a controlled way over a number of years so your body gets used to it and does not react to it so severely.