By Jamie Ee

Allergies have become more prevalent over the last few decades.

Scientists believe that improved living conditions, the rapid industrialisation of developing nations and a changing world climate are fuelling this trend, reported the World Allergy Organization.

In Singapore, the true prevalence of allergies is unknown, though it is estimated that about 15 per cent of the population suffers from airway allergies.

Some doctors here believe that it has reached a plateau in this city. Others believe they will become more common as the population grows more affluent and Westernised.

What is an allergy

Dr Leong Khai Pang, a senior consultant at the department of rheumatology, allergy and immunology in Tan Tock Seng Hospital, explained that people develop allergies when their immune system mistakenly identifies a substance - known as an allergen - as harmful, when it is usually not.

Virtually anything can be an allergen - from dust mites to fish to drugs.

It is not yet fully understood why some substances trigger allergies and others do not, nor why some people develop allergic reactions when exposed to allergens and others do not.

To develop an allergy, a person must first be exposed to the substance. Theoretically speaking, it is impossible to have an allergic reaction on the first encounter.

Once the body learns to recognise the allergen, the condition for an allergy is set up. On re-exposure to the allergen, the immune system becomes activated, producing an antibody called immunoglobulin E (IgE) that reacts with the allergen, which leads to an exaggerated immune response like runny nose, watery eyes and rashes.

Types of allergies

Generally, there are two ways to classify allergies. One is according to the nature of the allergen (drugs, food, environmental substances) while the other is by the body system it affects (whole body, skin, nose and lungs).

In Singapore, airway allergies like allergic rhinitis and asthma are usually triggered by proteins found in dust mites.

Food allergies, on the other hand, affect less than 2 per cent of the population, said DrLeong.

Allergies may develop at any age but certain allergies, like food allergies, appear to affect children more.

A study by the department of paediatrics at the National University of Singapore in 2004 estimated that about 4 to 5 per cent of children in Singapore have food allergies, compared to 1 per cent of adults.

Some allergies, like food allergies in children, disappear with time, though most allergies remain for life. It is uncertain why.

Dr Cheng Yew Kuang, a private consultant allergist at Gleneagles Medical Centre, said that about 85 per cent of food allergic children lose their sensitivity to most allergenic foods like eggs, milk, wheat and soya between the ages of three and five. However, if the food allergy is not resolved by the age of seven, it will most probably persist.

Who are at risk

Those with a family history of allergies have been found to be most susceptible to developing them.

If one parent has an allergic disease, the estimated risk of the child developing allergies is about 20 to 30 per cent, said Dr Cheng. When both parents have allergies, the risk increases to about 40 to 50per cent, he added.

An increase in allergen exposure, which leads to sensitisation, has also been identified as an important risk factor for the development of allergic disease though this is still being questioned today.

Some researchers believe that the way people live may affect their chance of developing allergies.

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