There is a common saying among the people that meat foods such as fish and shrimp are "hair products", which may cause rashes or itching after eating, especially carp. Indeed, fish and shrimp belong to hair.

Fish contains a lot of polyunsaturated fatty acids and fat-soluble vitamins, so most people regard it as healthy and delicious. However, a small number of people have symptoms such as long rash, itchy skin, red corners of the mouth, aggravated eczema, vomiting and diarrhea, and difficulty breathing after eating fish. In the folk, this kind of food that makes skin diseases relapse or aggravate is called "hair". From the point of view of modern medicine, these symptoms are probably due to allergies.

The real killer of fish allergy is albumin.

Fish allergy is generally food allergy mediated by IgE (immunoglobulin E). Fish allergy is more common in adulthood than in childhood. The more fish you eat, the more people are allergic. For example, the incidence rate in Asia is higher than that in Europe and America. Fish allergy is different from milk allergy, and it is often a lifelong allergy, similar to peanut allergy. 95% of fish allergies are mainly allergic to albumin in fish. Small albumin mainly exists in fish, and the content of small albumin in different fish varies greatly. This difference ranges from several times to hundreds of times, which explains why people who are allergic to fish have different allergic symptoms to different fish.

One study evaluated the content of small white protein in many kinds of fish, including salmon, trout, cod, carp, mackerel and herring. The content of small white protein per gram of fish is 2.5 mg of tuna, which is the highest. It can be seen that the albumin content of tuna and carp is hundreds of times different. Therefore, the same fish, allergic patients eat some fish without discomfort symptoms, while eating fish with high albumin content is prone to allergic symptoms. Specific to carp, because it is a fish with high albumin content, it is not surprising that it is prone to allergic symptoms after eating.

It was also found that the content of albumin in cooked fish samples could be reduced by 20% ~ 60%. In other words, the allergenicity of some fish may decrease after cooking, but it also means that albumin has thermal stability, that is, it may still be allergic after cooking fish into mud, even after frying and stewing.