Oysters are rich in nutrients and are called “milk of the sea,” but they are also known to cause food poisoning. It can be caused by a virus, bacteria, toxic plankton ingested while growing oysters, allergies, and many other things. People who get sick every time they eat oysters are most likely allergic to them, and should be aware of the dreaded symptoms such as anaphylactic shock. Here is a free illustration of an old man enduring abdominal pain and nausea among other symptoms.