Why does food allergy cause skin rashes?

The core reason why skin rash occurs after food allergy is that the allergens in the food trigger an abnormal response of the immune system, releasing inflammatory mediators that act on the blood vessels and nerves in the dermal layer of the skin, ultimately inducing a rash.

When I was on duty at the allergy clinic last week, I met a third-grade boy. When his mother brought him in, his arms and face were swollen red, and there were light scratches all over. After asking, I found out that he had stolen a classmate's peanut butter cookie on the way to school. He was already allergic to peanuts. After eating two mouthfuls, small red spots the size of needle tips began to appear around his mouth. In less than half an hour, they spread all over his body. He even had a lot of bulging wheals on his back. It was so itchy that he couldn't attend class.

Regarding the actual significance of allergic rashes, there are currently two different views in the industry. One group believes that this is a "clear alarm" given by the immune system. It is much easier to identify than latent allergies that only manifest as abdominal pain and chest tightness. It can help people quickly locate and avoid allergens, which in turn reduces the risk of subsequent severe allergies.； Another school of thought believes that skin rash itself is a "accidental injury" due to excessive immune activation. These inflammatory mediators were originally used to deal with invading pathogens, but in the end they were all used on harmless food proteins. Apart from making people itchy and restless, they did not help at all to remove allergens.

In fact, it’s easy to understand if you think of the immune system as the security team of a community. When encountering allergenic proteins such as milk, mango, and peanut for the first time, the security team misjudges it to be an “intruder.” They will note the characteristics of such proteins and generate the corresponding immunoglobulin E, which is what we often call IgE antibodies. Next time they encounter the same allergen, the anti- The body will immediately trigger an early warning and release a large amount of inflammatory substances such as histamine and leukotrienes. These substances travel along the blood vessels throughout the body. When they enter the skin, they will widen the gaps in the blood vessel walls. The blood plasma will seep into the dermis and form a red or white rash. It will also stimulate the surrounding nerve endings, so the rash is often itchy and makes people scratch it.

Many people also wonder why some people have diarrhea, others have asthma, and others only have a rash with the same food allergy. In fact, the "hardest hit areas" of immune response are different for different people. The blood vessels of some people's skin are more sensitive to inflammatory mediators, so they show up on the skin first. This kind of disease is relatively easy to judge. If you encounter a sensitive gastrointestinal tract, you may have diarrhea for several days without even thinking about what you are allergic to.

By the way, don’t underestimate these inconspicuous little red rashes. If the rash is accompanied by a tight throat, difficulty breathing, or even dizziness in front of your eyes, don’t bear it. This means that the allergic reaction has affected the respiratory tract and circulatory system. It may be a precursor to a serious allergy, and you need to go to the hospital immediately.