How do low pH and increased carbon dioxide affect hemoglobin’s ability to bind oxygen?

When the concentration of hydrogen ions increases (lowering the pH) or the concentration of carbon dioxide rises, the affinity of hemoglobin for oxygen decreases.1

This phenomenon, known as the Bohr effect, occurs because these substances bind to the hemoglobin molecule and induce structural changes that weaken its ability to hold onto oxygen. As a result, the oxygen-dissociation curve shifts to the right, meaning a higher partial pressure of oxygen is required to achieve the same level of hemoglobin saturation.12

This process is physiologically beneficial because it facilitates the release of oxygen to tissues that have high metabolic demands, such as during exercise, where increased carbon dioxide production and acidity signal a greater need for oxygen delivery. Conversely, when these concentrations are reduced, hemoglobin’s affinity for oxygen increases, shifting the curve to the left and enhancing oxygen binding.12