Vasoconstriction is narrowing or constriction of the blood vessels. It happens when smooth muscles in blood vessel walls tighten. This makes the blood vessel opening smaller. Vasoconstriction may also be called vasospasm.

When does vasoconstriction happen?

Vasoconstriction is the narrowing (constriction) of blood vessels by small muscles in their walls. When blood vessels constrict, blood flow is slowed or blocked. Vasoconstriction may be slight or severe.

Why does vasodilation and vasoconstriction occur?

Vasoconstriction is a response to being too cold. The process involves the narrowing of blood vessels at the skin surface to reduce heat loss through the surface of the skin. Vasodilation is a response to being too hot.