Whether food, respiratory or dermatological, allergies have been on the rise since the 1970s and even more so in the last 10 years. They particularly affect young children even though they can occur at any age. What are the causes? Research has some answers, although much remains to be done.
Allergies: risk factors
Until recently, allergists believed that allergies were hereditary and that an allergic terrain determined from birth could never disappear. Since the beginning of the 1970s, the upsurge in allergies has contradicted this hypothesis. Indeed, the accelerated development of allergies (allergic rhinitis, asthma, eczema etc…) could not be solely due to heredity. Today, researchers attribute this acceleration to the environment.
Western countries are those most affected by a strong development of allergies. Scientists therefore assume that it is the lifestyles and environmental conditions of these countries that are being called into question. Although scientists have not yet put the whole puzzle together, their conclusions are irrefutable.
According to Andrew Weil, Director of the Integrative Medicine Research Program (1) and Clinical Professor of Medicine at the University of Arizona, Tucson School of Medicine, “it is not possible to eliminate a hereditary predisposition to allergies, however it is possible to act on the immune system, by choosing an adapted lifestyle and modifying one’s environment.
Allergy is a response of the immune system to a supposed invasion of the body, so it is important to act so that the supposed enemy is again considered benevolent.”
Allergies: Genetic predispositions
Allergy occurs more often in genetically predisposed people, i.e. most of the time one or both parents suffer or have suffered from allergies. This is known as atopic or atopy. The risk of becoming allergic increases with family history, so the risk is 75% if both parents are allergic. It is 25 to 40% if only one of the parents is allergic.
When there is no family history, the risk is only 12-15%. Within the same family, allergic manifestations may be similar or different (eczema, hives, allergic rhinitis, allergic asthma) but are generally of the same category.
Interleukin-4 is one of the proteins that plays an essential role in allergic reactions. It increases the production of IgE antibodies, which promote the occurrence of embarrassing symptoms (oedema, breathing difficulties, rhinitis, cough). Scientists speculate that the predominance among African Americans of a gene that promotes the production of interleukin-4 may be the reason why they suffer from one of the highest rates of allergy and asthma in the United States.
Indeed, some studies show that African Americans have very high levels of interleukin-4. Some scientists link this predominance to the fact that their ancestors probably needed it to fight tropical parasites. This predominance remains today as these many interleukin-4 proteins now attack harmless allergens.
Allergies: Environment and lifestyle
Time and time again, researchers have found that groups of the same racial origin have radically different rates of allergy depending on the type of environment in which they live. In most cases, there has been a resurgence of allergies in affluent and urbanized environments. The pattern is true in Asia, where the highly urbanized Japanese are more allergic than the Chinese in rural areas. It is also true in Africa, where metropolitan residents are more allergic than people living in the bush.
One of the most telling studies was conducted in Germany, just after the reunification of East and West Germany. According to Harold Nelson, a physician and researcher at the National Jewish Medical Centre in Denver, it found that West Germans, who were wealthier than their East German cousins, suffered far more allergies than their East German cousins.
This finding was to dispel the assumption that pollution, to which East Germans were much more exposed than West Germans, was a major contributor to the development of the allergy epidemic. However, apart from the case of passive smoking indoors, which effectively increases the risk of asthma in children, the involvement of air pollution in the development of asthma and other forms of allergy is not proven.
On the other hand, there is a strong correlation between allergies and other environmental factors such as socio-economic status, family size, early childhood infections and diet.
If there was any doubt that the environment was not a driving force in allergy, what happened in the former East Germany in the 10 years following reunification helps to remove it. The capitalist model became the norm there, the standard of living increased dramatically and with it the allergy rate. Today, the whole of Germany is struggling with extremely high rates of allergies.
When scientists identified allergy as a disease of western life, they thought the explanation was simple: houses are full of all kinds of things, including indoor pollution, pets and processed foods. We first thought that the increasing prevalence of asthma was related to the quality of indoor air in homes (better insulated, overheated or humid, not enough air is being replaced) or to the location of the home (crowded buildings, semi-detached houses, etc.),.
There is no doubt that indoor air quality in homes has deteriorated with westernization. Everyone thought they had found the global answer. Then we started to see situations where that didn’t fit. As proof, Nelson cites European studies showing that infants exposed to dogs or cats at home developed 50% fewer allergies than children from homes without pets. It was from this observation that the hygiene hypothesis was born.
The hygiene hypothesis indicates that our overly sanitized Western lifestyle keeps the immune system uncertain, unbalanced and unable to distinguish between friends and enemies. Researchers believe that much of this confusion begins in childhood. There is strong evidence that a baby’s immature immune system can only develop properly when exposed to bacteria from fermented foods.
Premature exposure to antibiotics, on the other hand, seems to create the wrong stimulus by upsetting the balance between friendly and hostile bacteria. The result is an increased risk of allergies. The challenge for scientists is to understand how the overly sanitized Western lifestyle, genetics and the environment combine to create allergies. But since two of these three factors are controllable, there is great hope that one day allergy sufferers will be able to live (almost) like everyone else.