Who gets allergies?

There are several factors which determine whether someone may be susceptible to allergies. It is likely to be an inherited characteristic. Studies have shown that if one parent is atopic, then there is a 25 – 40 % chance that the child will also be atopic. If both parents are atopic, the risk of the child being atopic rises to 50 – 75 %. However, no specific gene for allergies has been identified in humans.

It is also believed that children who are brought up in cleaner environments are more susceptible to suffering from allergies. This does have a scientific basis – more TH2 cells (a type of T helper cell) are thought to be produced in people who are less exposed to bacteria and viruses. Likewise, more TH1 cells are thought to be produced in people who are more exposed to bacteria and viruses. TH1 cells and TH2 cells can counteract and moderate the effects of each other. TH2 cells are involved in stimulating B lymphocytes to become plasma cells and release antibodies, and if there are more TH2 cells active, then more antibodies (in this case, IgE) can be produced.

The severity and timing of the allergy can be subject to other factors:

• The age at which you are first exposed to the allergen has an effect on how severe it can be. If you are exposed to an allergen in the first few years of life, you are more likely to become allergic to it. Allergies which start in childhood can improve as you get older. Allergies can also be gained later on in life (such as occupational asthma).
• Any infections at the time of first exposure to the allergen, or exposure to to any other irritants (such as pollution from diesel engines and cigarette smoke) at that time can also make allergies more severe or increase the chances of becoming allergic to a specific allergen, by damaging internal linings and allowing more of the allergen to penetrate the body and sensitise mast cells.
• Underlying immune disorders can also have a part to play in how severe allergies can be. For example, individuals with a weak immune system (immunodeficiency) have a higher chance of developing allergies. This is probably because the body cannot repair itself as efficiently and thus, allergens can penetrate body tissues and sensitise more mast cells. It may also be due to poor regulation of IgE production by TH1.

Allergies Guide Index:

• What are allergies?
• What's the difference between allergies, intolerance, and sensitivity?
• Overview of the immune system
• How do allergies happen?
• Who gets allergies?

• What are some common symptoms of allergies?
• What are some common allergies?
• How can I check to see what I'm allergic to?
• What treatment options are available?