Blue baby syndrome can refer to a number of conditions that affect oxygen transportation in the blood, resulting in blueness of the skin in babies. Historically, the term "blue baby syndrome" has referred to babies with one of two conditions: Both of these conditions cause cyanosis, or a bluish discoloration of skin or mucous membranes. Normally, oxygenated blood appears red and deoxygenated blood has more of a blue appearance. In babies with low levels of oxygen or mixing of oxygenated and deoxygenated blood, the blood can have a blue or purple color, causing cyanosis.