Lye, chemically known as sodium hydroxide or potassium hydroxide, is a strong alkali with a dual role in skin care. In its raw form, it is extremely hazardous and corrosive, posing a severe threat upon contact with human tissue. Despite this danger, lye is a necessary component for creating beneficial personal care products, most notably true soap. Understanding the difference between raw lye and its transformed state is key to determining if this chemical is beneficial for your skin.
Why Raw Lye is Caustic and Dangerous
Raw lye, whether sodium hydroxide (NaOH) for solid products or potassium hydroxide (KOH) for liquid ones, is a highly corrosive base with a very high pH, typically ranging from 13 to 14. This extreme alkalinity makes it dangerous to organic tissue. When lye contacts the skin, it immediately begins liquefaction necrosis, resulting in a chemical burn.
The strong alkali quickly dissolves the fats and proteins that make up the skin and cell membranes. This reaction is similar to soap making, but here the lye reacts with body tissue, causing damage. Unlike acid burns, lye burns continue to penetrate deeper into the tissue, causing severe, slow-healing injuries. If raw lye contacts the skin, the affected area should be flushed with copious amounts of water for at least 15 minutes while seeking immediate medical attention.
The Essential Chemical Process of Saponification
Lye is an indispensable ingredient in true soap creation because it is the alkali required for saponification. This process involves mixing the lye with triglycerides, which are fats or oils derived from plants or animals. When the lye solution is introduced to the fats, it breaks the triglyceride molecules apart.
The reaction chemically transforms the lye and the oils into two new substances: soap (a fatty acid salt) and glycerin (an alcohol). This transformation is complete; in a properly formulated product, all of the original caustic lye is consumed and no longer exists in its dangerous, free form. Sodium hydroxide creates hard bar soaps, while potassium hydroxide produces softer or liquid soaps.
The precise ratio of lye to oil is carefully calculated to ensure all the alkali is used up in the reaction. A slight excess of fat, known as “superfatting,” is often added to guarantee no lye remains and ensures the finished product is mild and contains residual moisturizing oils. The soap must cure for several weeks after the initial reaction, allowing saponification to fully complete and excess water to evaporate, resulting in a stable and safe cleansing product.
How Lye Enables Beneficial Cleansing Products
The finished product of saponification, true soap, provides significant benefits to the skin. Soap molecules are unique because they have one end that attracts water and another that attracts oil. This structure allows them to effectively emulsify dirt, oil, and grime from the skin’s surface, making soap a foundational component of hygiene.
The second byproduct of saponification, glycerin, is important for skin hydration. Glycerin is a humectant, meaning it draws moisture from the air and the skin’s deeper layers to the surface, helping to keep the skin moist and soft. Unlike many commercially processed soaps where glycerin is removed for separate sale, artisan-made soaps retain this natural moisturizer.
Finished, cured soap is safe to use because it is no longer caustic, typically exhibiting a mildly alkaline pH between 9 and 11. Although this pH is higher than the skin’s natural slightly acidic pH of about 5.5, the brief contact time during washing does not cause lasting damage. The benefit comes not from the lye itself, but from the completely transformed, mild, and moisturizing soap and glycerin that the lye enables.