Formation of non-functional methaemoglobin causes blue-baby syndrome. This is due to

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Blue baby syndrome is blood related condition found in babies due to nitrate poisoning (poisoning limits blood's ability to carry oxygen thereby causing baby to look blue); known as metheamoglobanemia. This is a serious illness in infants which is caused when nitrate is converted into nitrite in the infant's body. Nitrite interferes with the oxygen carrying capacity of the child's blood (It replaces the oxygen on the red blood cells). This is an acute disease in that symptoms can develop rapidly in infants.