The cause of food allergies is related to your immune system. Your immune system is your body’s main defence system against infection.
The immune system
The immune system protects the body by producing specialised cells called antibodies. These are the ‘hunter-killer’ cells of the body.
Antibodies identify potential threats to your body, such as bacteria and viruses. They then signal to your immune system to release chemicals to kill the threat and prevent the spread of infection.
In food allergies, a type of antibody known as immunoglobulin E (IgE) mistakenly targets a certain protein found in food as a threat to your body. The next time you come into contact with that food, the IgE antibodies trigger the release of a number of chemicals, of which the most important is histamine.
Histamine causes most of the typical symptoms that occur during an allergic reaction. For example, histamine:
- causes small blood vessels to expand and the surrounding skin to swell,
- affects the nerves in the skin, which can cause the skin to feel itchy, and
- increases the amount of mucus produced in your nose lining, causing local itching and burning.
In most allergic reactions to food, the release of histamine is limited to certain parts of the body, such as your mouth, throat or skin.
In anaphylaxis, the immune system goes into ‘overdrive’ and releases massive amounts of histamine into your blood. This causes in the wide range of symptoms associated with anaphylaxis.
Possible risk factors
Exactly why the IgE antibodies mistakenly target harmless food proteins is uncertain. However, a number of risk factors for food allergies have been identified, which are outlined below.
Food allergies, particularly peanut allergies, seem to run in families. If you have a parent, brother or sister with a peanut allergy, you are seven times more likely to develop a peanut allergy than someone with no family history of the condition.
This suggests that some food allergies, particularly peanut allergies, may be caused by specific genes that you inherit from your parents.
Other allergic conditions
Children who are born with other allergic conditions, such as asthma or atopic dermatitis (an allergic skin condition), are more likely to develop a food allergy.
The rise in food allergy cases
Another puzzling aspect of food allergies is that the number of cases has risen sharply over the past two decades. For example, the number of children admitted to hospital for food-related anaphylaxis has risen by 700% since 1990.
There are a number of theories about this sharp increase, which are outlined below.
Changes in diet
One suggestion is that dietary changes in the western world may be responsible for the dramatic increase in the number of food allergy cases.
Some experts think that the increase in food allergy cases may be due to a decrease in the consumption of animal fats, such as butter and lard, and a corresponding increase in the consumption of vegetable fats and oils, such as margarine. The implication is that vegetable fats and oil may stimulate the over-production of IgE antibodies.
Another diet-related theory is that the decrease in the consumption of fresh fruit and vegetables may be responsible for the increase in food allergies.
These types of foods contain antioxidants, which are substances that help protect against cell damage. It is possible that a lack of antioxidants during early childhood may interfere with the normal development of the immune system in some children.
A third theory is that a reduction in Vitamin D in the diet may be responsible for the increase in food allergies. Vitamin D is found in oily fish, beef, cheese and eggs. It can also be produced naturally through the effects of sunlight on the skin.
Rates of food allergies are higher in countries that are nearer the North Pole, which may be due to a reduced exposure to sunlight.
Currently, there is no hard evidence to support (or disprove) any of these theories.
The hygiene hypothesis
Another theory for the significant increase in the number of food allergy cases in recent years is that children are increasingly growing up in ‘germ-free’ environments. This means that their immune system may not receive sufficient early exposure to the germs that it needs to develop properly.
This is known as the hygiene hypothesis. This hypothesis has also been suggested as the reason for the rise in other allergic conditions, such as asthma. However, as with the diet-related theories, there is little hard evidence to support or disprove the hygiene hypothesis in relation to food allergies.