By Jamie Ee

There are many different types of allergies and they can trigger different reactions:

Environmental allergy

Allergens in the environment, when inhaled, may trigger asthma and allergic rhinitis. Allergic rhinitis refers to the inflammation of the lining of the nose due to allergy. Symptoms include runny or blocked nose, sneezing and nose itch.

However, not all rhinitis and asthma are caused by environmental allergens, said DrLeong Khai Pang, a senior consultant at the department of rheumatology, allergy and immunology at Tan Tock Seng Hospital. Common environmental allergens include:

House dust mites: In Singapore, the most common environmental allergen is house dust mites. Up to 80 per cent of patients who suffer allergic reactions have house dust mite allergy. They especially thrive in high humidity and in areas where human dander (dead skin flakes) are located - like bedding, carpets and soft toys. The allergen is found in their droppings.

Pets: It's not the fur but rather a protein found in the saliva and dander of the animal. They are invisible particles in the air.

Grass and tree pollen: In Singapore, the common ones include oil palm pollen and resam fern (a common jungle plant) spores.

Mould: The allergen is in the spores released by moulds which thrive in damp areas of the house like bathroom windows.

Cockroaches: The allergen is in the droppings of the cockroach.
Treatment may include using a nasal spray to prevent and treat the inflammation in the nasal lining. Oral antihistamines may also be used to relieve itching, sneezing and a runny nose. Immunotherapy to environmental allergen is also another mode of treatment.

--------------------------------------------------------------------------------
Food

These are generally more common in children than in adults.

A study by the department of paediatrics at the National University of Singapore in 2004 estimated that about 4 to 5per cent of Singaporean children and 1 per cent of adults suffer from food allergies.

Among children in Singapore, the study also showed that the most common food allergens are bird's nest, crustaceans such as prawns (Photo 3) and crabs, eggs and cow's milk.

Among adults, another local study showed that shellfish and bird's nest were the most common allergens.

In contrast to Western studies, peanuts and tree nuts are not a common cause of food allergy in both children and adults here. The reason is uncertain but TTSH's Dr Leong said studies suggest that it could be due to the way the nuts are manufactured.

Dry roasting peanuts, which is common in Western countries, increases allergenicity, compared to boiling or frying peanuts, which is more common in countries like China and Singapore.

(Page 1 of 2)Other common food allergens include soya, wheat and fish.

The symptoms of food allergy range from mild skin symptoms like flushing, itching, hives and swelling around the eyes, lips and face, to symptoms involving internal organs and systems like light-headedness, loss of consciousness, difficulty in breathing, vomiting and diarrhoea, to severe anaphylactic reactions which are sudden and may cause death.

While food allergies in childhood are usually transient - most lose them from three to five years old. Allergies acquired in adulthood usually persist.

Food allergies acquired in childhood, which do not disappear by the age of five to seven are likely to persist for life.

There is no cure for food allergies. For patients with severe anaphylactic reaction, strict avoidance, including hidden sources in food, is of paramount importance in addition to carrying an epinephrine auto-injector.

--------------------------------------------------------------------------------
Drug allergy

A study by the department of rheumatology, allergy and immunology at Tan Tock Seng Hospital in 2003 showed that about four in 1,000 inpatients here suffer from drug allergies.

According to the study, the most common drugs that triggered allergic reactions were antibiotics (penicillins, cephalosporins, cotrimoxazole) and anti-epileptic drugs (phenytoin and carbamazepine).

--------------------------------------------------------------------------------
Insect venom allergy

People who are allergic to the venom of stinging insects like honey bees (Photo 4), wasps, and ants can develop a severe or even life-threatening reaction or anaphylaxis.

Cold compresses, oral painkillers and antihistamines are used to treat pain and swelling. However, people who develop anaphylaxis after a single insect sting should be evaluated for immunotherapy. This is because immunotherapy is highly effective and can reduce the chance of a reaction to less than 3per cent.

--------------------------------------------------------------------------------
Latex allergy

The most common cause of latex allergy is through direct contact with latex, such as by wearing latex gloves (Photo 5) or by contact with latex-containing products like balloons, rubber toys, erasers and condoms. Latex products, especially gloves, shed large amounts of latex particles, which can become airborne.

This causes itching, redness, swelling, sneezing or a runny nose and can lead to anaphylaxis.

--------------------------------------------------------------------------------
Nickel allergy

Nickel allergy is commonly associated with earrings and jewellery for other body piercings. However, nickel can also be found in many everyday items like coins, necklace clasps, watchbands and spectacle frames.

Dr Lim Yen Loo, an associate consultant dermatologist at the National Skin Centre, said the prevalence of nickel allergy is estimated to be around 20 per cent and there seems to be a trend of increasing incidences over the years.

This story was first published in Mind Your Body, The Straits Times, on Dec 4, 2008.

For more The Straits Times stories, click here.