Nitrates are harmful because they react with hemoglobin, converting it into a molecule known as methemoglobin. Methemoglobinemia can lead to severe pain and neurological damage if not treated immediately. Children are particularly at risk because their bodies are still developing, so any impairment of oxygen transport could have serious long-term consequences. In infants, nitrate poisoning usually results from eating vegetables contaminated with nitrogen-rich fertilizer or manure. The vegetable matter passes through the digestive system undigested, allowing the nitrates to be released and absorbed by the body. Symptoms include headache, irritability, poor appetite, stomach pain, diarrhea, and potentially serious complications including hypothyroidism and neurodevelopmental problems. A blood test can be used to check for signs of nitrate poisoning. Treatment includes removing the child from danger, cleaning out the stomach, and giving them lots of fluids. In an emergency, nitroglycerin may be used to dissolve some types of methemoglobin.