What Is Calcium Hydroxide?
Calcium hydroxide, also called calcium dihydroxide or slaked lime, is an inorganic compound with the chemical formula Ca(OH)2. It starts its life in nature as calcium carbonate found in limestone or chalk. When these rocks are heated at high temperatures they release carbon dioxide and leave behind calcium oxide, better known as quicklime. Adding controlled amounts of water to quicklime produces calcium hydroxide, which is then purified, dried and milled into a fine white powder for cosmetic use.
The material’s use goes back thousands of years in construction and food preparation, but it gained a foothold in beauty routines during the twentieth century, first in traditional depilatory pastes and later in professional hair relaxer systems. Today manufacturers value calcium hydroxide mainly as a pH adjuster, allowing them to fine-tune formulas that would otherwise be too acidic. You will most often spot it in hair relaxers, depilatory creams, clay masks, certain exfoliating treatments, some lotions and occasional specialty serums where precise pH control is critical.
Calcium Hydroxide’s Cosmetic Benefits/Uses
In topical products calcium hydroxide serves one primary role:
Buffering – By keeping a formulation within a narrow pH range it protects fragile actives, helps preservatives work efficiently and makes sure the finished product feels comfortable on skin or hair. Stable pH also minimizes irritation, extends shelf life and maintains the intended texture and viscosity of creams and gels.
Who Can Use Calcium Hydroxide
In the low concentrations found in most retail cosmetics calcium hydroxide is generally tolerable for normal, combination and oily skin. Very dry or sensitive skin may feel stinging or tightness when the surrounding formula is not properly buffered, so people in those categories should pay closer attention to how their skin feels after application. Anyone with broken skin, eczema or other barrier impairments should avoid products that list calcium hydroxide high on the ingredient list because the alkalinity can amplify discomfort.
The ingredient is mineral based and produced without animal derivatives which makes it suitable for vegans and vegetarians.
No data suggest that calcium hydroxide poses a special risk to women who are pregnant or breastfeeding when used as directed in topical products. This is not medical advice and anyone who is expecting or nursing should still clear new skincare or haircare products with a qualified healthcare professional.
Calcium hydroxide does not increase photosensitivity so it will not make skin more prone to sunburn. It also has no known hormonal or comedogenic activity.
Potential Side Effects/Adverse Reactions
Responses to topical calcium hydroxide vary by individual. The following lists potential side effects that could occur although most users will not experience them when the ingredient is properly formulated and used as directed.
- Skin redness, itching or burning
- Dryness or tightness due to temporary disruption of the skin’s acid mantle
- Contact dermatitis in people who are allergic or highly sensitive
- Chemical burns when high concentrations remain on skin for prolonged periods
- Brittleness or breakage of hair shafts if the product is left on too long in relaxer systems
If any of these reactions develop stop using the product immediately and consult a healthcare professional.
Comedogenic Rating
Rating: 0/5. Calcium hydroxide is an inorganic alkaline powder that dissolves or disperses in water rather than forming an oily film on skin or blocking pores, so it has no tendency to trigger comedones. It is therefore considered non-comedogenic and is generally suitable for people who are prone to acne or breakouts. Because its main job is pH control, it is usually present at very low levels that rinse or absorb away easily, leaving nothing behind that could clog follicles. One thing to note is that it is sometimes combined with petrolatum or other occlusive bases in depilatory creams or hair relaxers; in those cases pore blockage would be due to the companion ingredients, not the calcium hydroxide itself.
Summary
Calcium hydroxide functions almost exclusively as a buffering agent. By moderating alkalinity it stabilizes active ingredients, supports preservative systems and helps products keep the intended texture and feel. It does this by releasing hydroxide ions that raise or hold pH at a precise level, preventing formulas from drifting too acidic over time.
While it is a workhorse behind the scenes, calcium hydroxide is not particularly trendy in daily skincare and is most often found in professional hair relaxers, depilatories and the occasional clay mask or exfoliant where strict pH control is crucial. Its safety profile is solid when used in the low concentrations allowed in cosmetics, though higher strengths used by professionals demand careful timing and removal.
Most people tolerate it well but, as with any new product, a patch test is wise to confirm your individual response and avoid surprises.