A complete analysis of seafood allergies: Which one is more risky, shrimp, crab or shellfish?

Judging from the clinical admission data of domestic allergy departments in the past five years, the overall risk of allergy to shellfish is higher than that of shrimp and crab. However, this order is not absolute. The demographic results of people in different regions and different eating habits will be significantly different. Some studies even believe that the order of allergy in different age groups is also different. There is no completely unified conclusion in the industry.

Last week, I met a 22-year-old girl in the clinic. She had swollen lips after eating prawns, which disappeared in a few hours. She never took it seriously. Last week, she ate half a charcoal-grilled oyster during a company team building. Within ten minutes of swallowing it, she said her throat was tight and she couldn't breathe. My colleague took her to the emergency room and gave her epinephrine to relieve her symptoms. After checking the allergens, the shellfish-specific IgE value indeed soared to level six, which is more than three times higher than the allergenic value of shrimp.

Of course, not everyone conforms to this rule. I also have a 50-year-old patient who has been eating clams and scallops for decades without any problems. But if he touches a bite of drunken shrimp, he will be covered in wheals, which makes him itchy and unable to sleep all night long. This is actually related to the frequency of dietary exposure in different regions. Statistics from European and American countries show that shrimp allergy rates are the highest. After all, they eat shrimps from cold waters all year round, and their exposure is much higher than shellfish, so the data are naturally different.

In fact, the main allergens of shrimp and crab are tropomyosin, which is very stable. Even if it is cooked at high temperature for half an hour, it will still cause sensitization. This is equivalent to giving the "identification mark" to immune cells. The cross-reaction rate between shrimp and crab can reach more than 70%, which means that if you are allergic to shrimp, you will most likely be affected by eating crab. In addition to tropomyosin, shellfish also has several allergenic components such as arginine kinase and troponin. The scope of cross-reaction is wider. Even many people who are allergic to dust mites and cockroaches may trigger allergies when they eat shellfish for the first time. This is actually caused by cross-sensitivity.

Many people think that "if I had no problem eating seafood before, I will always be fine." This idea is really bad. Last year, I treated an older brother who had eaten hairy crabs for 20 years and was fine. Last year, he ate a mouthful of crab meat half a month after COVID-19, and he went directly to the emergency room. Allergy is actually a "mistake" of the immune system. If you have stayed up late, been under great stress, just got sick, and have a disordered immune system, your former "old friends" may also be attacked as "intruders".

There are also many people who feel flushed, dizzy, and have diarrhea after eating seafood. This is not necessarily true. If you eat stale seafood, a similar reaction will occur if there is too much histamine in it. This is called histamine poisoning, and it is not an immune-mediated allergic reaction. If you eat fresh seafood next time, it will be fine. Don’t scare yourself into thinking you are allergic.

If you really suspect that you are allergic to seafood, you will not be able to try "eat a small amount and slowly desensitize" randomly. Especially if you have experienced severe reactions such as difficulty breathing and tight throat, it is best to prepare an epinephrine pen in your bag when going out.