When you have a headache after eating crab, consider whether there is a food allergy, food poisoning, or seafood poisoning. You can first simply boil a bowl of ginger soup to warm the stomach and disperse the cold and relieve pain, and drink patchouli water or patchouli pills, which can also improve the symptoms of headache and cold in the stomach, because crab is cold. If the symptoms do not improve after a day or two, and you still have headache, along with nausea, vomiting, diarrhea or fever, you need to seek prompt medical attention. Checking routine blood and stool at the hospital to see if there are changes in white blood cells, neutrophils and lymphocytes in the blood and white blood cells in the stool routine is a problem of infection in the gastrointestinal tract, which needs to be treated with sedation if necessary. However, if the symptoms are mild and not very acute, using ginger soup, patchouli water or with Chinese herbs will completely solve the symptoms.