Allergy: Common allergies - text only -

• Bee and wasp stings

• Hay fever

• House mites

• Pets

• Food

• Bee and wasp stings
Nobody likes being stung. The swift injection of venom when a bee or wasp stings causes an unpleasant reaction in everyone. Most people experience localised itching, pain and swelling. But a few people (less than 1% of the population) experience a severe allergic reaction. This can include losing consciousness, breathing harshly or wheezing, a swollen throat or tongue, dizziness or fainting, and falling blood pressure.

If you're at risk, sensible advice to avoid being stung includes wearing shoes when walking in grass and avoiding rubbish bins, perfumes and brightly coloured clothing, which all attract insects. It's also a good idea to keep an allergy kit with you at all times, just in case (see Allergic Reactions). Severe allergic conditions can be treated with a course of injections which desensitise the body to insect venom.

• Hay fever
Not everyone greets the first warm breezes of summer with unbridled joy. For some, these breezes bear the irritants that will keep them sneezing all summer. Tiny grains of wind-borne pollen, released by trees and grasses to fertilise other plants, fill the air. In a good summer — and a bad hay fever season — the pollen count can rise dramatically: from 1,000 grains of pollen per cubic metre of air to 8,000 per cubic metre. When the air that you breathe (about ten cubic metres a day) makes your eyes itch and your nose stream, it is difficult to escape. Yet this is a condition — also known as seasonal allergic rhinitis — with which more than nine million people in the UK have to cope.

• House mites
Through a chink in the curtains, a sliver of morning sun casts a sunny patch across an unmade bed, and illuminates dancing motes in sunlight. A lovely, homely image? Not really. The dancing motes are in part dead bugs, whose children, and whose children’s children, are still alive and breeding snugly in the duvet, the mattress, the pillows and the carpet. These are house-mites, microscopic organisms which make their homes in bedding and upholstery. In normal circumstances, the winter cold should kill them off, but modern heating provides year-round warmth in which house mite populations thrive.

House mites produce protein waste products which cause an allergy similar to that experienced by hay fever sufferers. But it is worse, in that it lasts all year round. In fact, house mite allergy is thought to be the most common cause of perennial allergic rhinitis.

• Pets
Cat and dog hairs have long been blamed for allergic reactions to pets and the homes of pets. However, researchers have discovered that proteins secreted by oil glands in animals’ skin, and found in animal saliva and urine, are the main cause of an allergic reaction to animals. Cats may cause a greater allergic reaction than dogs because they lick themselves more frequently. When their saliva dries, the proteins are released into the air, getting up people’s noses and down their throats, bringing on the sneezing and itching that typify airborne allergies.

• Food
In children, the most common food allergies are associated with eggs, milk and peanuts, whereas adults most commonly have allergic reactions to shellfish, peanuts, walnuts, fish and eggs.

Food allergies are caused by proteins in food that are not broken down by cooking or digestion. The proteins are therefore free to cross the stomach and intestine linings and enter the bloodstream, where they can circulate, causing reactions throughout the body in an allergic person.

The process of digestion affects the timing and the location of a reaction. A person who has eaten food to which they are allergic may experience itching in the mouth while they are eating. Later, as the food is digested in the stomach, they may start to experience abdominal pain, vomiting and diarrhoea. When the proteins cross into the bloodstream, there maybe a drop in blood pressure, and when they reach the skin, hives or eczema may develop. This reaction occurs rapidly, within a few minutes to an hour.

If a food allergy is life-threatening, a sufferer will usually be advised to avoid similar foods as these may trigger the same reaction. For example, a person who is allergic to prawns may be advised to avoid crab, lobster and crayfish too.

The immune system | Common allergies

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