The Bohr shift effect states that the oxygen binding ability of hemoglobin is inversely proportional to the pH level of the blood and the concentration of carbon dioxide within it.
Hemoglobin transports oxygen to the various tissues of the body and removes carbon dioxide from the tissues. The mechanism by which hemoglobin is able to transport the gases was first described by the scientist Christian Bohr. He found that when the pH is decreased (acidic environment), hemoglobin will be unable to retain its oxygen molecules. The pH of a fluid environment can be decreased by increasing the production of carbon dioxide, producing carbonic acid in this case.
Tissues use oxygen for various metabolic processes and produce carbon dioxide. The carbon dioxide produced reacts with water molecules to release protons and decrease the pH of bodily fluids. This decrease in pH acts as a signal that oxygen is being used in the tissues and that carbon dioxide is building up. When oxygenated hemoglobin from the lungs reaches the metabolically active tissue, the lower pH caused by the higher concentration of carbon dioxide causes a release of oxygen. The "shift" in Bohr's effect refers to the shift in the binding characteristics of hemoglobin to oxygen at a physiologically normal pH (7.4) compared to the more acidic pH in metabolically active tissue (7.2).