You can think of it is a buffer that helps keep membrane fluidity from getting too high or too low at high and low temperatures. ... In this case, cholesterol in the membrane has the opposite effect and pulls phospholipids together, increasing intermolecular forces and decreasing fluidity.

How does cholesterol affect the fluidity of membranes?

Cholesterol acts as a bidirectional regulator of membrane fluidity because at high temperatures, it stabilizes the membrane and raises its melting point, whereas at low temperatures it intercalates between the phospholipids and prevents them from clustering together and stiffening.

Does cholesterol make membrane more or less fluid?

At high temperatures, cholesterol interferes with the movement of the phospholipid fatty acid chains, making the outer part of the membrane less fluid and reducing its permeability to small molecules.