Allergy
ICSE Class 7 · Biology · Chapter 7
What this chapter covers
- What an allergy is
- Allergens: the substances that set off allergy
- How allergens enter the body
- Symptoms of allergic reactions
- Seasonal and perennial allergies
- Precautions and care for a person prone to allergies
Key definitions
Allergy is an unusually strong reaction of the body's defence system to a substance that is harmless to most people.
Allergens are substances that cause an allergic reaction in a person who is sensitive to them.
House dust is a mixture of many tiny things: soil, fibres from clothes and carpets, flakes of dead skin, hair, bits of insects and the droppings of very small creatures.
Dust mites are tiny eight-legged animals, related to spiders, that live in house dust and feed on the flakes of dead skin that people shed every day.
Pollen grains are the tiny, powder-like grains produced by the flowers of plants for reproduction.
Irritants are substances like these that harm or inflame the lining of the nose, throat or air tubes directly, without an allergic reaction.
Symptoms are the changes a person feels or shows in the body when something is wrong with it.
Hay fever is the common name for an allergy to pollen that causes sneezing, a runny nose and itchy, watering eyes.
Asthma is a condition in which the small air tubes inside the lungs become narrow and swollen, making breathing difficult and noisy.
Seasonal allergy is an allergy whose symptoms appear only during a particular season of the year and disappear for the rest of it.
Perennial allergy is an allergy whose symptoms can appear at any time of the year because the allergen is present all year round.
Key points
- Allergy is an unusually strong reaction of the body's defence system to a substance that is harmless to most people.
- Allergens are the substances that cause allergic reactions; the allergy is the reaction itself.
- Common allergens include house dust, dust mites, pollen grains, mould spores, strong sunlight and particular foods such as nuts, milk, eggs and prawns.
- Allergens enter the body through the nose, the mouth and the skin.
- Symptoms include sneezing, a runny or blocked nose, itchy watering eyes, wheezing, rashes, hives, swelling of the lips and stomach upsets.
- A sudden severe reaction with swelling and difficulty in breathing is an emergency that needs immediate medical help.
- Seasonal allergies appear only at certain times of the year, mostly due to pollen; perennial allergies can appear at any time, mostly due to indoor allergens such as dust mites.
- Allergies are not infectious, but they often run in families.
- The best care is to find the allergen and avoid it: keep the home clean and dry, avoid pollen and irritants such as smoke, check food labels, protect the skin and take only prescribed medicines.