In people with allergy or asthma, their conditions may worsen if exposed to substances or situations, called “triggers”.

The most common triggers and allergens are airborne. They include plant pollens, indoor and outdoor moulds, waste from house dust mites, materials shed from animals (dander), foods, and insects.

Inflammation of the upper and lower airways in response to one or more triggers or allergens causes the most common symptoms. As a result of inflammation, the airways may also become overly sensitive, making them more likely to react the next time they encounter that trigger.

Researchers have also shown that exposure to some triggers may play a part in the development of asthma and allergy in the first place.

Non-allergen triggers include cold air, exercise, colds and viruses, tobacco smoke, pollution, exhausts, perfumes, airborne fumes from chemicals, paints or cleaners, and emotional stress.