Blue-baby syndrome in children is caused due to nitrate poisoning called Methaemoglobinaemia. When drinking water, rich in nitrates is consumed, nitrates are converted into nitrites by microbial flora of intestine. These nitrites then combine with the haemoglobin of blood to form met heamoglobin, which interfere with the oxygen carrying capacity of the blood and leads to damage in respiratory system, circulatory system and blue colouration of skin and even cancer.