The harm of roundworms can be divided into two parts: the larval stage and the adult stage. After the larvae of roundworm are absorbed through the intestine, they can enter the lungs with the blood circulation, causing symptoms of allergic pneumonia such as chill, fever, cough, blood in sputum, and urticaria, etc. In severe infection, the larvae can enter the large circulation through the pulmonary capillaries and invade the thyroid gland, lymph nodes, thymus gland, spleen, brain and spinal cord, and then cause symptoms in the corresponding parts. Adult roundworm parasites in the intestine can cause nausea, vomiting, abdominal distention and pain, loss of appetite, intermittent periumbilical pain or epigastric cramps. Children can also develop convulsions, teeth grinding, and heterophagia, which can then affect their growth and development. Ascaris can also cause some serious complications, such as ascaris intestinal obstruction, biliary ascariasis, appendicular ascariasis and even intestinal perforation.