Allergy is a disease influenced by genetic factors. Is not the antigen that is inherited, but only the generic preparation. In other words, a parent with allergies, for example, the pollen will have children and grandchildren who are allergic to dust mites are allergic to animal hair, and so on. Allergies result from abnormalities of different chromosomes of polygenic DNA , it is assumed that some of these are also the regulators of asthma, in both cases, the bronchial hyperactivity as a symptom has also often these genetic alterations lead all'iperproduzione immunoglobulin IgE , which is what happens with the immediate hypersensitivity (type I). The likelihood of developing an allergy IgE-mediated in a child where both parents are atopic is around 40-60%, with no atopic parent is reduced to 5-10%. The risk of developing an allergy then increases as the number of relatives with the disorder.
Parallel to genetics, environmental factors play an important role in the onset of atopy invest. A recent theory, called the "Hygiene Hypothesis", indicates the excess of hygiene one of the causes that promote the onset of allergy. It is shown that an environment (or food) too "sterile" is not healthy for the immune system becomes more prone to developing allergies. Among the various observations endorse this hypothesis it was found that in children living in rural areas or who have a cat in the house (shown in the first two years of life), the likelihood of allergy is reduced significantly. Food allergies are less common among those who are in close contact with fecal microbes, or food, because the bacterial flora of these individuals is full of microbes that produce endotoxins , which inhibit the production of allergenic proteins, which would otherwise stimulate the gut by increasing the odds of asthma and rhinitis allergic. In Western countries, the early use of antibiotics in children, the widespread use of chemical additives in foods and their sterilization, seem to delay the development of the bacterial flora.
Predisposition to the development of allergy is also related to the birth month. In spring, in fact, the plants release their pollen, while in autumn there is a greater frequency of mites, so early exposure to these allergens leads to a greater likelihood of a future development of atopy. As for smoking, it is uncertain whether it is a risk factor for the development of atopy as early as the pregnancy, but it certainly increases the odds of developing asthma and respiratory diseases, has also been proven that children of smoking mothers or exposed to secondhand smoke develop a greater quantity of IgE.
Finally, a diet based on fatty acids are vegetable oils such as predisposition seems to atopy, although the opinions are divided, while breastfeeding can delay the contact with other allergenic agents not contained in breast milk, while also providing immune defenses are essential for the child.
Among respiratory infections, one that certainly offers greater predisposition atopy in preschool or grade school, is the bronchiolitis from RSV ( Respiratory Syncytial Virus ), RSV stimulates the production of protein sensitization.
One can therefore say that allergies are most affected by those who belong to upper class, they are only children, live in urban areas and maintain high standards of hygiene.