Cholesterol
Properties
| State | Solid at room temperature (waxy) |
| Color | White crystalline solid |
| Solubility | Insoluble in water; soluble in organic solvents and fats |
| Melting Point | 148 °C |
| Boiling Point | 360 °C (decomposes) |
About Cholesterol
Cholesterol is the parent sterol of mammalian biochemistry — four fused rings (three cyclohexanes and a cyclopentane in the steroid nucleus, the so-called gonane skeleton), one double bond between C5 and C6, an isooctyl side chain off C17, and a 3-beta hydroxyl that's the only polar group on an otherwise hydrocarbon-like molecule. That asymmetric polarity is what makes it function in membranes: the OH sits at the bilayer interface alongside the phospholipid phosphates while the ring system intercalates between phospholipid acyl chains, restricting their conformational mobility. The result is a membrane that's neither too fluid (above the phospholipid melting point) nor too rigid — cholesterol holds it in the liquid-ordered phase, and animal cells without cholesterol literally cannot maintain membrane integrity. Your liver synthesizes it via the mevalonate pathway, the same pathway that statins block by inhibiting HMG-CoA reductase, the rate-limiting enzyme. About 1 g/day of cholesterol gets made endogenously, which is roughly 4-5x the dietary intake on a typical diet. Cholesterol is also the biosynthetic starting point for every steroid hormone in mammals — pregnenolone via CYP11A1 is the gateway, and from there the pathway branches to progesterone, cortisol, aldosterone, testosterone, and the estrogens — plus bile acids (about 0.5 g/day cycled through the enterohepatic circulation) and vitamin D3 via the 7-dehydrocholesterol intermediate. The Brown and Goldstein work on the LDL receptor that pulls cholesterol-loaded LDL particles out of plasma won the 1985 Nobel and laid the groundwork for the entire statin pharmacology that followed.
Where you'll encounter it
If you've had a lipid panel drawn, the total cholesterol number is the sum of the cholesterol carried in LDL, HDL, and VLDL particles in your plasma — and the LDL number specifically is what cardiovascular risk calculators use because LDL particles deposit cholesterol into atherosclerotic plaques. In a research lab, cholesterol shows up as the membrane-mimic component in liposome and supported-lipid-bilayer experiments — a typical bilayer for protein reconstitution might be 70:30 POPC:cholesterol mol/mol to mimic mammalian plasma membrane composition. Cholesterol is also the substrate for cholesterol oxidase in the standard clinical chemistry assay: oxidation produces H2O2, which is detected by a peroxidase-coupled colorimetric reaction.
Common Uses
- Membrane fluidity modulator in liposome and supported-lipid-bilayer biophysics experiments
- Biosynthetic precursor for all mammalian steroid hormones, bile acids, and vitamin D3
- Standard analyte and calibrator in clinical chemistry total-cholesterol and HDL/LDL fractionation assays
- Substrate for cholesterol oxidase in coupled enzymatic assays for serum cholesterol quantification
- Emulsifying agent in pharmaceutical creams, ointments, and lipid-based drug delivery vehicles
- Component of pulmonary surfactant replacement formulations for neonatal respiratory distress
- Reference compound for steroid mass spectrometry and isotope-dilution clinical methods
- Starting material for industrial semisynthesis of progesterone and other steroid pharmaceuticals
Safety Information
Pure cholesterol as a chemical reagent is essentially non-hazardous to handle — no GHS classification beyond mild eye and skin irritation from the powder, no acute oral toxicity at any practical dose, and no PEL set by OSHA. The clinically relevant hazard is the serum LDL cholesterol concentration: epidemiology consistently links LDL above 160 mg/dL to elevated cardiovascular risk, and statins targeting HMG-CoA reductase are prescribed to drop it below 100 mg/dL (or below 70 in patients with established disease). Dietary cholesterol intake matters less than the saturated-fat content of the diet because endogenous synthesis adjusts to absorbed cholesterol via SREBP-2 feedback regulation, which is why the 2015 US Dietary Guidelines dropped the long-standing 300 mg/day dietary cholesterol limit. The 2025-vintage understanding is that genetic LDL handling and saturated fat intake dominate the risk equation.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.