Why do children develop food allergies?

The current general consensus in pediatric clinical and immunological circles is that the essence of food allergy in children is a failure to establish immune tolerance. The immune system mistakenly identifies harmless food proteins as foreign invaders and initiates an uncomfortable reaction caused by an excessive immune response. The core inducement is the joint effect of innate genetic susceptibility and acquired environmental exposure.

I have been working in the children's health department for almost 8 years and have met hundreds of children who come to see the doctor because of food allergies. The most common question asked by parents is "Neither of us are allergic, so why is the baby allergic?" ”In fact, it is not surprising. Heredity is only a susceptibility factor, not 100% of the disease. I have seen families where both parents have allergic rhinitis. Both children are severely allergic to eggs and milk. The oldest child has bloody stools when drinking ordinary formula milk when he was a child. The second child has swollen around the mouth as soon as he adds egg yolk. I have also seen children whose parents have no history of allergies who are allergic to peanuts due to improper feeding.

In the past, our feeding concept has always been that "the later you add allergenic things, the better". Even the guidelines from more than ten years ago clearly recommended that eggs should be added after 1 year old, and peanuts and nuts should be 3 years old before touching them. However, with the accumulation of clinical data over the years, this view has long been overturned - after 2016 The WHO and pediatric associations of various countries have updated their guidelines, clearly recommending that high-risk babies with a family history of allergies can gradually introduce small doses of eggs, peanuts and other allergenic foods after adding complementary foods for 6 months. Continued small amounts of exposure can help the immune system "recognize" these proteins and reduce the probability of allergies. I treated a 3-year-old boy last month. His parents were afraid that he would be allergic. After almost two years of supplementary food, he only dared to give him bland food such as porridge, pumpkin, and yams. He had never touched eggs or nuts. As a result, he ate a bite of a classmate’s peanut cake during the autumn outing in kindergarten. He broke out in hives all over his body and couldn’t breathe. He was sent to the emergency room to check for allergens. The IgE antibodies corresponding to peanuts were so high that he missed the golden period of building tolerance.

Regarding the causes of allergies in children, there is a widely circulated saying that "allergies occur if the home is too clean." This actually corresponds to the "hygiene hypothesis" in the field of immunology. This view believes that too few microorganisms are exposed to early in life, and the immune system is not trained enough, so it is easy to attack harmless food proteins. Research data shows that children who grow up in rural areas and are often exposed to livestock and soil are more likely to have food allergies. The probability is about 30% lower than that of urban children who have been in a disinfected and clean environment for a long time. However, many studies do not support this conclusion. They believe that daily household cleaning will not affect immune development at all. What really increases the risk of allergies is the abuse of antibiotics in early life, cesarean section without exposure to maternal birth canal flora, and pure formula feeding without access to the immune regulatory factors in breast milk. The blame cannot be dumped on "cleanliness" in general.

To put it bluntly, a child's immune system is like a new security guard who has just taken up the job. He meets a lot of people in the early days and can naturally tell who is the owner and who is an outsider. If he is not allowed to meet strangers, he will be treated as a gangster and surrounded by people who come to deliver express. Allergies are actually an oolong caused by the immune system. There are still many controversial points, such as whether to deliberately avoid foods during pregnancy to reduce the risk of allergies in children. The conclusions of different studies are different. The mainstream recommendation is that unless the pregnant mother is allergic to a certain food, she does not need to deliberately avoid allergenic foods and can just eat a normal diet.

Don’t be too anxious if you encounter a child with a food allergy. Most mild to moderate food allergies will slowly build up tolerance as the child’s immune function gradually improves as they grow older. Only a small number of them will last until adulthood. Find a doctor to clarify the allergen and avoid it. If necessary, cooperate with intervention. Don’t be overly nervous.