Although the dead crab will produce some harmful ingredients, it is too late for the newly dead crab bacteria to multiply in large quantities, and some ingredients such as cadaverine and histamine cannot be produced, so the newly dead crab is edible. However, the time of death is too long. For example, at the high temperature of more than 30 degrees, crabs have been dead for more than four hours and soaked in unclean water. You can't eat in this situation.

Protein of crab contains more histidine, which is decomposed and metabolized by a large number of bacteria to produce histamine. Histamine can change the permeability of blood vessels, and macromolecules can easily enter the tissue through the blood vessel wall and cause allergies. People with sensitive constitution are allergic to eating crabs containing histamine.

The histamine content in skin mucosa, lung, large intestine and other parts is very high, and the edema tissue fluid is rich. Eating it will cause tissue edema, which may lead to bronchiectasis and allergic asthma.