2, crabs grow in the rivers and mud flats or seashore, like to eat animal carcasses and other rotten food, so its body surface and digestive tract are full of bacteria, viruses, parasites and toxic debris. If the crabs die, these bacteria will multiply greatly and decompose the rich histidine in the crabs, producing many histamine and histamine-like substances. Histamine is a toxic substance, adults can be poisoned when they eat 100-150 milligrams of histamine at a time.

3, histamine poisoning incubation period is very short, 5 minutes after eating can appear symptoms, the longest is only 1 hour, generally more in 0.5-1 hours onset. The patient first feel lips, throat discomfort, face and upper body flushing, eyes see congestion, very much like a drunk. At the same time, palpitations, rapid pulse, dizziness, headache, chest tightness, dry mouth, tongue numbness, dysphagia and other symptoms.

4, produce a large number of histamine dead crabs, although the general steaming can kill the bacteria on the surface and in the digestive tract, but histamine and other toxic substances can not be destroyed, so eating can cause histamine poisoning. Therefore, river crabs must buy live, sea crabs are dead, but must pick fresh. It is best not to buy dead crabs, and don't eat them after they are cooked to avoid food poisoning.