What is an Allergy?

What is an Allergy?

Allergies are very common and affect about one in three New Zealanders at some stage in their life. There are many different causes of allergies, and symptoms can range from very mild to severe and life-threatening. Allergies are one of the major factors associated with asthma.

When does an allergic reaction occur?

An allergy occurs when a person's immune system over-reacts to exposure to a substance (allergen). These allergens are found in house dust mites, pets, pollens, foods, moulds and insect stings, etc. An allergen for one person may not be a problem for another person, and everyone reacts differently.

What happens to my body when I have an allergic reaction?

Antibodies are supposed to protect our bodies against viruses, parasites, and infections. But for people with an allergy, their immune system mistakenly identifies the particular allergen as an invader and begins to create an exaggerated allergic response to it. These antibodies (IgE) attach themselves to mast cells and other immune regulatory cells (T-helper cells etc). When the allergen is encountered it triggers the mast cells and other immune regulatory cells to release specific substances, including histamines. The effect of these released substances causes an allergic reaction.

This reaction often occurs within minutes or up to a few hours after contact and may lead to many different symptoms from very mild to extremely severe.

What symptoms will I experience when having an allergic reaction?

Symptoms of an allergic reaction may depend on where the allergen enters your body. An airborne allergen such as pollen, for example, is breathed in through the nose and usually causes symptoms in the nose, eyes sinuses and throat.

Food allergy, on the other hand, is more often associated with stomach or bowel problems but may affect the rest of the body.

The symptoms of allergic reactions range from mild to severe and life-threatening. They can be categorised to the organs affected, which are:

  • Skin - hives, eczema and facial swelling
  • Respiratory System - symptoms can affect the nose (hay fever), throat (swelling) and lungs (cough, wheeze, bronchospasm)
  • Gastrointestinal System - nausea, vomiting, stomach pains and diarrhoea
  • Cardiovascular System - feeling faint, weakness, pallor, floppiness (particularly in infants), and collapse

Allergic symptoms may only occur locally - for example, localised swelling to a bee sting - or they can be generalised (widespread) affecting other body systems.

An anaphylactic reaction is where a generalised allergic reaction affects the respiratory and/or cardiovascular systems, as well as the skin and/or gastrointestinal systems.

What are common allergens in New Zealand?

The most common causes of allergic reactions in New Zealand are:

  • Dust mites
  • Grass pollens
  • Cats and other animals,
  • Food, such as peanuts, cow's milk protein, egg and soy
  • Insect stings
  • Moulds

Allergen Triggers

Airborne triggers are commonly dust mites, pollen, mould spores, and cat and dog allergens. Skin contact or inhalation of an airborne allergen can lead to symptoms of skin rash, swelling of the eyes, hay fever and asthma. Airborne allergens are not often a trigger for anaphylaxis.

Food allergens are most often ingested. Any type of food can trigger an allergic reaction. The majority of allergic reactions are triggered by egg, cow's milk, peanuts, tree nuts, soy, wheat, seeds, fish and shellfish.

Egg and dairy are the most common trigger in infants

Peanuts, tree nuts and seafood are the most common triggers in older children, teenagers and adults

Food may trigger reactions that range from localised contact reactions of the lips/mouth/tongue, to generalised reactions, including anaphylaxis.

Insect venom is an injected allergen from stinging insects such as bees and wasps. The venom from each of these insects is different, and being allergic to one doesn't mean you will be allergic to others. Reactions range from localised reactions, which can be large and last for a number of days, to immediate generalised reactions, including anaphylaxis. Because a sting punctures the skin, anaphylaxis can be rapid, within minutes.


< Back to Waikato Allergy Clinic

Scroll to Top