Cholesterol is one of the dominant steroid molecules found in eukaryotic organisms, allowing the control of membrane fluidity. On its insertion into the membrane, fluidity increases due to the straightening and de-tangling of the fatty acid tails. As cholesterol causes the straightening of the fatty acid tails of the membrane lipids, the membrane becomes wider where there is a higher proportion of cholesterol.
High levels of cholesterol can result in plaques forming in the circulatory system, increasing the likelihood of clot formation - this can be an issue in the brain, where ischaemia can be fatal.