What is the pH of human blood?

What is the pH of human blood? Human blood has a normal pH of about 7.4.

More precisely, normal arterial blood is usually maintained between pH 7.35 and 7.45, so 7.4 is the standard rounded answer used in general science quizzes. This narrow range is slightly alkaline rather than neutral: neutral pH is 7.0 at standard conditions. Blood pH is regulated because many proteins and enzymes work properly only within a limited acid–base range.

The lungs and kidneys provide the main long-term controls. The lungs adjust carbon dioxide removal through breathing; dissolved carbon dioxide contributes to carbonic acid, so faster ventilation can reduce acidity. The kidneys help by excreting hydrogen ions and managing bicarbonate, an important blood buffer. Together, these systems form part of the body's acid–base homeostasis.

A common mistake is treating 7.4 as an exact, unchanging value. Blood pH naturally fluctuates within its narrow range, and values below 7.35 are generally described as acidosis while values above 7.45 indicate alkalosis. Even small departures can be medically significant, which is why blood-gas tests report pH with considerable precision.