The Truth About Peanut Allergy: Why Tiny Exposure Can Cause Shock

The threshold for shock in patients with peanut allergy is as low as you can imagine - a minimum of 100 nanograms of peanut allergen protein is required, which is equivalent to one millionth of the weight of an ordinary peanut. The essence is that the immune system treats harmless peanut protein as a deadly invader and initiates an extreme defense mode of indiscriminate attack.

Last month, I picked up a 12-year-old girl from the emergency room in the allergy department. My mother cut her a piece of toast with a knife spread with peanut butter in the morning. She felt her throat tightened after just one bite. She fell down in the elevator when she went downstairs. When she was delivered, she was covered in hives and her blood pressure could not be measured. It took almost an hour to stabilize her. The girl's mother sat at the emergency door crying and said that she only knew she was allergic to peanuts before, but she didn't know that bread touched by a knife dipped in peanut butter could cause harm.

Many people think this is because the patient is "squeamish", but this is not true. You must first understand the logic of peanut allergy. If our immune system has been exposed to peanut protein before and misjudges it to be a harmful substance, it will produce IgE antibodies specifically against it. These antibodies are like "radar" attached to the surface of mast cells and basophils, waiting to catch allergens. However, several major allergenic proteins in peanuts are particularly stubborn. It is difficult to destroy their structure even through baking or gastric acid digestion. Even if only a little bit leaks into the blood circulation, as long as it bridges with two or more IgE antibodies, it is equivalent to directly igniting the mast cells and releasing all the inflammatory substances such as histamine and leukotrienes stored in the cells into the blood in a few seconds.

As soon as these inflammatory substances come out, the blood vessels throughout the body will instantly expand, the gaps in the blood vessel walls will also become larger, and the water in the blood vessels will leak into the tissues. The blood volume originally running in the blood vessels will suddenly be insufficient, and the blood pressure will plummet. At the same time, the mucous membranes of the throat and airways will also be edematous, making the person unable to breathe. This is anaphylactic shock. If the whole process is fast, it can be fatal in a few minutes, and there is no way to wait for medical treatment.

However, as to why more and more people are allergic to peanuts, the academic community is still arguing. In the past few years, everyone believed that "it is not good to introduce complementary foods early" and said that children should wait until they are 1 year old before eating peanuts. However, the 2015 LEAP study directly overturned this conclusion and said that adding a small amount of peanut products to high-risk children between the ages of 4 and 6 months can reduce the risk of allergies by 70%. Now the complementary food guidelines in various countries have changed. There is also a group of people who support the "hygiene hypothesis", saying that homes are too clean now, children have not been exposed to enough microorganisms when they were young, and the immune system has nothing to do, so it treats food protein as its enemy. However, some studies do not agree with this statement and think it is more related to the structural characteristics of peanut allergenic protein itself. There is no accurate estimate yet.

I have also met many family members asking, is it okay as long as they don’t eat peanuts? Really not. There was a hypersensitive patient who used a hand cream containing cold-pressed peanut oil given by a relative. His hands were swollen for three days. Some people also have attacks when they are exposed to dust from other people eating peanuts on closed high-speed trains or airplanes. Therefore, it is not an exaggeration for people with severe peanut allergies to carry an epinephrine pen with them. It is a life-saving thing.