Stearic Acid (Octadecanoic Acid)

Stearic acid (first syllable pronounced either steer or stair) is the saturated fatty acid with an 18 carbon chain and has the IUPAC name octadecanoic acid. It is a waxy solid, and its chemical formula is C18H36O2, or CH3(CH2)16COOH.


  • Stearic acid is useful as an ingredient in making candles, plastics, dietary supplements, oil pastels and cosmetics, and for softening rubber.
  • It is used to harden soaps, particularly those made with vegetable oil. Stearic acid is used in aerosol shaving cream products.
  • Stearic acid is also used as a parting compound when making plaster castings from a plaster piece mold or waste mold and when making the mold from a shellacked clay original. In this use, powdered stearic acid is dissolved in water and the solution is brushed onto the surface to be parted after casting. This reacts with the calcium in the plaster to form a thin layer of calcium stearate which functions as a release agent.
  • It is used along with simple sugar or corn syrup as a hardener in candies.
Stearic Acid (MSDS) (2,48 MB)