Ingredient dictionary
Calcium Hydroxide
Also listed as: Slaked lime
Calcium hydroxide is a white mineral powder that is strongly alkaline. In beauty products, it mainly raises pH, the acid-to-alkaline scale, and helps with hair straightening. Checked against our library November 6, 2026.
What Calcium Hydroxide does
- Raises the pH of a formula
- Helps keep formulas in their working range
- Works alongside guanidine in some relaxers
Calcium hydroxide is made by adding water to calcium oxide, also called quicklime. The result is a fine white powder, often called slaked lime, that is strongly alkaline. It is not very soluble in water, so it is typically mixed into a cream or base rather than dissolved on its own.
Formulators mostly use it to raise pH, which helps keep a formula in the range where its other ingredients work well. Its best-known beauty role is in hair-straightening creams, where it works alongside guanidine carbonate to help loosen the bonds that give hair its curl. Use those products strictly as directed on the pack.
Good for
Most useful for shoppers reading hair-straightening labels, where it does a specific job, and for anyone curious how pH-adjusting bases work.
Frequently asked questions
Is calcium hydroxide safe in skincare?
At the levels used to adjust pH in creams and lotions, it is generally well tolerated. Its strong alkalinity means hair-straightening products, which are designed for a specific use, need strict directions. Patch test any product if your skin is sensitive.
What is calcium hydroxide used for?
Mainly to raise pH, so a formula sits in its working range. It also has a role in some hair-straightening creams, alongside guanidine carbonate. It is not used as a moisturizer.