Allergy: Allergic people - text only -

• The hygiene theory

• Pollution

• Family traits

• The Allergic March

Allergy is spreading throughout the population at an alarming rate. At present, one in four British people suffer from an allergy, or have done at some time in their lives. Each year, the number of UK allergy sufferers increases by 5%. Over the past 20 years, the number of people with allergies has increased fourfold. More than nine million of us suffer from hay fever, and more than one million people suffer from a food allergy.

The reasons behind the spread of allergies are not fully understood. This is not surprising, because we don't fully understand why some people are susceptible to allergies and others are not. We don't know, for example, why males are more likely to become allergic than females are, or why small families are more allergy-prone than larger families.

But in general, theories tend to link the allergy epidemic to our over-protected Western lifestyles and increased air pollution.

• The hygiene theory
Scientists believe that the seeds for allergies are sown in childhood. When we are children, we all have a tendency to manufacture E-antibodies. Gradually, through exposure, the body learns to differentiate between invasions by parasites and invasions by bacteria and other infections. It learns to make other antibodies. But in the case of children who are over-protected from dirt and disease, it is thought, the body never learns to make these other antibodies to deal with infections and bacteria. In contrast, living on a farm, particularly a livestock farm, is thought to prevent allergies developing, because of exposure to certain bacteria. The hygiene theory explains why people with a Western lifestyle are more likely to develop allergic reactions.

• Pollution
Scientists believe that over-exposure to some types of dirt and air pollution may also promote allergies. The environment during the first year of a child's life is thought to be crucial. If a child is exposed frequently to cigarette smoke, pets, pollen and other potential allergens, they are more likely to develop allergies later. There is evidence connecting air pollution with a number of respiratory disorders, as well as conditions such as eczema. Air pollutants in house dust are also thought to be a major factor in the development of allergies.

• Family traits
For some people, neither the right upbringing nor clean air will suffice to protect them from allergy. People with atopy, an inherited condition which increases the likelihood of developing allergies, are genetically predisposed to suffer from conditions such as asthma, eczema, hay fever and hives. Not all atopic people will develop these conditions, but they are more likely than other people to do so.

• The Allergic March
'The Allergic March' is the term used to describe the way in which allergies develop over a person's lifespan. Not all allergies last a lifetime, and some occur earlier than others. Children under the age of three are most likely to suffer from food allergies and eczema. Allergy to egg white is common at this age, but is unlikely to persist beyond the earliest years of life. Asthma is most common in pre-pubescent children; hay fever is most common in adolescence. Some allergies, such as food allergies developed in adulthood, are likely to last for life, however.

The immune system | Common allergies

Allergic reactions | Allergic people

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