What is Allergy

Allergy or an allergic reaction is a term used to describe an adverse immune reaction to a protein (or allergen) in our environment, which is normally harmless to the non-allergic person. Hypersensitivity reaction is a term commonly used by doctors to describe the same phenomenon.

Symptoms and signs of an allergic reaction depends on the part of the body affected. They can range from mild skin itch to full-blown anaphylaxis and death. Only a small proportion of the population exposed to an allergen will develop an allergic reaction. Peanut allergy and wasp stings are good examples.

Allergy develops after repeated exposure to the causative allergen. Sensitisation takes place on initial exposure and usually no adverse reaction appears to occur during this phase. Some time later on repeated allergen exposure, the full-blown allergic reaction will develop.

During sensitisation, Immunoglobulin E (IgE) antibodies for specific allergen are produced by our white blood cells. On re-exposure, these IgE antibodies bind the allergen and attach to mast cells, which release Histamine leading to an allergic reaction. Late phase reactions may follow 6 to 24 hours later with Inflammation and tissue swelling.

Some people may become sensitised to an allergen and have positive allergy tests but not ever had an allergic reaction. These individuals go about their lives completely oblivious to this fact.

"Non-allergic" hypersensitivity (or intolerance reaction) are more common and do not involve the immune system. Good examples include headaches triggered by chochlette and fast heart beat caused by caffeine.

Types of allergies

There are a wide variety of substances that can cause allergic reactions. Some of the most common include:

• Food (most commonly peanuts, tree nuts, dairy, egg, soy, wheat, fish and shellfish)

• Pollens and moulds

• Stinging insects

• Animals

• Dust mites

• Drugs

• Latex

Who is at risk?

Children may inherit the tendency to develop allergies if either parent or any family member suffers from eczema, asthma, hay fever, hives, allergic rhinitis, persistent cough, constant runny nose, food allergies or recurrent ear infections.

The specific allergy is not inherited from the parents, merely the tendency to be allergic.

If neither parent is allergic there is still a 5-15% chance that the child will develop allergies. For a child with allergic parents, this increases to 25%. If both parents are allergic there is a 50-60% chance of developing allergies. When both parents have the same allergic disease the risk increases to 80%.

The likelihood a child will develop an allergy depends on both the genetic family history and environmental factors. Children must be exposed to a particular allergen in order to become sensitised. Once sensitivity has been established, it can take very little contact with the allergen to cause a reaction and the child is also at risk of becoming allergic to other allergens.

Is Allergy on the increase?

Yes!

Treatment for allergic conditions is the most common reason people visit their GPs.

In the last ten years, the privately run Auckland Allergy Clinic has seen allergy prevalence increase by 50%. Public practice has seen an increase from 40 patients per month 2 years ago to 150-200 per month today. There is a waiting list of 8 months.

The sale of allergy related drugs is also increasing. Antihistamines and nasal sprays have increased 6.3% between 1999 and 2000, and a further 1.2% to present.

Allergy New Zealand received 7500 inquiries in 1998, this rose to 90,000 in 2000 and to more than 100,000 so far in 2002. Membership in the organisation has increased 60% over the last 3 years.

Why is allergy increasing?

There are probably many factors influencing the rise in allergic disease. The reasons for the increase are being widely researched.

It is now generally accepted that allergy is a developed country phenomenon; it doesn't exist in third world countries. There seems to be a connection between standard of living and allergy; the better our homes and living standards are, the more allergies we have. There is a definite relationship between low levels of exposure to infectious disease in babies and young children and an increased prevalence of allergies.

To put it simply, the immune system doesn't have enough to do in the hygienic environments we have created. If the developing immune system doesn't have sufficient diseases to combat, it begins to react to the allergens it comes in contact with first and most often. Typically in a baby that is food, either through infant formula or the introduction of first foods too early.

Sometimes even the minute quantities of food proteins that pass through breast milk are enough to sensitise an infant.

Our diets have changed dramatically in the last 50 years; we are eating more complex foods than our predecessors. Babies today are fed foods that weren't available many years ago.

Our warm, well-insulated, thickly carpeted homes may also play a significant role. This type of environment is the perfect breeding ground for dust mites, microscopic creatures that live in our bedding and carpets. The dustmites themselves are harmless, but their droppings are highly allergenic and exposure in infants and children can lead to the development of allergies like asthma, eczema and rhinitis.

There is also evidence that overuse of antibiotics in the first years can lead to a higher risk of developing allergies.

Can allergies be prevented?

There are some steps that can be taken to reduce the likelihood that a child will inherit his or her parents' allergies.

Sensitisation can occur in utero. During pregnancy, it can be helpful for a mother-to-be to reduce her exposure to allergens around the home like pets and dust mites, and to irritants such as tobacco smoke. It is also recommended that, where there is a family history of allergies, women avoid eating peanuts, tree nuts and shellfish when pregnant. This recommendation is also worth following when breastfeeding, as minute amounts of food allergens can pass through the breast milk.

Breastfeeding has been shown to be protective against the development of allergies.

Delaying the introduction of the major food allergens (peanuts, nuts, dairy, egg, wheat, soy, fish and shellfish) and minimising a baby's exposure to allergens around the house (dust mites, pets and moulds) may help prevent allergic sensitization although there is still on-going discussion amongst scientists and researchers on whether these measures are effective or not.