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Why can physical exercise temporarily raise a person’s white blood cell count?

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Illustration of a blood vessel with a cutaway view showing red blood cells, white blood cells, platelets, and plasma, each labeled to highlight the main components of blood. — white blood cell Blood is made up of multiple components, including red blood cells, white blood cells, platelets, and water-rich plasma.

Physical exercise can cause a temporary increase in a person’s white blood cell count, a condition known as leukocytosis.12

This rise occurs because intense physical exertion acts as a physiological stressor on the body. During such stress, the body may release catecholamines—such as epinephrine—which are hormones that help initiate a rapid response to physical demands. This hormonal shift, along with other physiological changes associated with strenuous activity, leads to a transient increase in the number of white blood cells circulating in the bloodstream.12345

It is important to note that this fluctuation is a normal, temporary response to physical activity rather than a sign of disease. Once the exertion ceases and the body returns to a resting state, the white blood cell count typically stabilizes.512