Methemoglobinemia is a condition in which the blood contains an abnormally high level of methemoglobin, a form of hemoglobin that is unable to bind oxygen. Some synonyms for methemoglobinemia include "oxidized hemoglobinemia," "ferric hemoglobinemia," and "metHbemia." Methemoglobinemia can have a variety of causes, including exposure to certain medications, chemicals, or toxins, as well as genetic mutations that affect the production or function of the enzyme responsible for converting methemoglobin back to normal hemoglobin. Symptoms of methemoglobinemia can include shortness of breath, headache, fatigue, and cyanosis (a bluish discoloration of the skin). Treatment typically involves administration of oxygen, intravenous medications, or a blood transfusion to lower methemoglobin levels.