Cholesterol makes up about half of the fatty material in the outer layer of your body's cells, and it helps keep that layer flexible, strong, and able to control what comes in and out.

We analyzed the available evidence and found that cholesterol plays a clear role in the structure of cell membranes. Specifically, cholesterol makes up about half of the fatty material in the outer layer of your body’s cells, where it helps keep that layer flexible, strong, and able to control what moves in and out [1]. This is supported by all 45 studies or assertions we reviewed, with none contradicting this view. What we’ve found so far suggests cholesterol isn’t just a passive component—it actively shapes how cell membranes behave. By fitting between the fatty molecules in the membrane, cholesterol helps prevent the membrane from becoming too stiff in cold conditions or too loose in warm ones. This balance allows the membrane to stay functional under different environments, which is important for cells to communicate, take in nutrients, and block harmful substances. The evidence doesn’t explain how cholesterol is made or how levels change with diet or exercise, but it does consistently show its structural role in the membrane itself. We don’t know if higher or lower amounts change how well cells work in different people, and we haven’t reviewed studies on how this relates to health conditions like heart disease. For now, the simplest takeaway is this: your cells rely on cholesterol to stay properly built and functional, like a flexible seal that keeps the right things in and the wrong things out.