Sodium hydroxide shows up in a surprisingly wide range of products, from the drain cleaner under your kitchen sink to the bar soap in your shower. Also known as lye, caustic soda, or white caustic, this strong alkaline chemical serves different purposes depending on the product: dissolving grease, adjusting pH, breaking down organic material, or triggering chemical reactions that transform raw ingredients into finished goods.
Household Cleaners
Cleaning products are where most people encounter sodium hydroxide directly. It’s a core ingredient in drain openers and clog removers, where it dissolves hair, grease, and soap buildup inside pipes. Oven cleaners rely on it to break down baked-on food and carbonized grease. You’ll also find it in toilet bowl cleaners, hard water stain removers, stovetop cleaners, and some general-purpose household cleaners.
These products tend to contain higher concentrations of sodium hydroxide than anything else in your home. Drain cleaners in particular can be extremely caustic. If you check the label, you might see it listed as “sodium hydroxide,” “lye,” “caustic soda,” or “soda lye,” so it’s worth knowing all the names.
Soap and Bar Soap
Every traditional bar of soap starts with sodium hydroxide. The soapmaking process, called saponification, involves mixing lye with fats or oils. The sodium hydroxide triggers a chemical reaction that converts those fats into soap. Here’s the reassuring part: a properly made bar of soap contains zero free sodium hydroxide. The lye is fully consumed during the reaction, so the finished product is completely safe for your skin.
You may still see sodium hydroxide on bar soap ingredient lists because manufacturers are required to disclose the raw ingredients used in production, even if the chemical no longer exists in its original form in the final product. Liquid soaps typically use a related chemical, potassium hydroxide, instead.
Hair Relaxers and Personal Care Products
Sodium hydroxide is the active ingredient in many chemical hair relaxers, where it works by breaking the protein bonds that give hair its natural curl pattern. Brands like Mizani, Silk Elements, Revlon Realistic, and Motions all make relaxer formulations containing it. These are sometimes called “lye relaxers” to distinguish them from “no-lye” alternatives that use different alkaline chemicals.
Beyond relaxers, sodium hydroxide appears in some body exfoliants and scrubs, where it’s used in small amounts to adjust pH. Chemical peels and certain cosmetic formulations also use it as a pH adjuster, typically in concentrations far lower than what you’d find in a cleaning product. In these products, it’s not the star ingredient. It’s a behind-the-scenes tool that keeps the formula at the right acidity level.
Drinking Water
Municipal water treatment plants commonly add sodium hydroxide to your tap water, and it’s one of those facts that sounds alarming until you understand why. Water utilities use it to raise pH, soften water by removing mineral hardness, and control corrosion in pipes. Typical treatment concentrations range from 2 to 100 milligrams per liter, though poor-quality source water may require more.
The sodium hydroxide reacts with the water and dissolved minerals, so it doesn’t arrive at your tap in its original caustic form. The amount of sodium it adds to your drinking water is generally insignificant. Water treatment facilities prefer it over alternatives like lime or soda ash because the dosing systems are simpler and require less maintenance.
Food Processing
Several foods you eat regularly are processed with sodium hydroxide. Pretzels get their distinctive brown, glossy crust from a lye bath before baking. Olives are cured in a sodium hydroxide solution to remove their natural bitterness. Lutefisk, a traditional Scandinavian dish, is dried fish rehydrated in lye. Hominy and the masa used in tortillas are made by soaking corn kernels in an alkaline solution, a process called nixtamalization.
In commercial food production, sodium hydroxide is also used to peel fruits and vegetables, process cocoa and chocolate, and thicken ice cream. As with soapmaking, the chemical is either washed away or neutralized before the food reaches you.
Paper, Textiles, and Other Industrial Products
Sodium hydroxide is one of the most widely used industrial chemicals in the world, and it touches products you’d never suspect. In the pulp and paper industry, it plays a role at nearly every stage. During pulping, it dissolves lignin, the natural glue that holds wood fibers together, making it possible to separate and refine cellulose fibers. During bleaching, it breaks down impurities to produce lighter, whiter paper. It’s even used in deinking recycled paper, effectively dissolving old ink so the fibers can be turned into new products.
The textile industry uses sodium hydroxide in scouring and bleaching processes that remove impurities and increase the whiteness of fibers. Cotton in particular is treated with lye in a process called mercerization, which gives fabric its characteristic sheen and improves dye absorption.
The list of industries that depend on sodium hydroxide extends well beyond paper and textiles. It’s used in oil and gas refining, metal processing, pharmaceutical manufacturing, synthetic rubber and resin production, biofuel processing, mining and mineral extraction, soil remediation, and wastewater treatment. If a manufacturing process needs a strong base to dissolve organic material, adjust pH, or drive a chemical reaction, sodium hydroxide is often the go-to choice.
How to Spot It on Labels
Sodium hydroxide goes by several names on product labels. The most common alternatives are caustic soda, lye, soda lye, and white caustic. If you’re scanning ingredient lists on cleaning products, cosmetics, or food packaging, any of these terms refers to the same chemical.
On cosmetic and personal care labels, you’ll typically see “sodium hydroxide” spelled out. On industrial or cleaning products, “lye” and “caustic soda” are more common. Food labels may list it as “sodium hydroxide” or simply reference a lye treatment in the product description.
Safety Around High-Concentration Products
The products that pose the greatest risk are the ones with high concentrations: drain cleaners, oven cleaners, and industrial-strength formulations. Contact with concentrated sodium hydroxide causes severe chemical burns to skin and eyes. Inhaling fumes can inflame the lungs and cause throat swelling. Swallowing it damages the esophagus and stomach, with tissue destruction that can continue for weeks after exposure.
If sodium hydroxide gets on your skin or in your eyes, flush the area with large amounts of water for at least 15 minutes. Speed matters with chemical burns, so start rinsing immediately rather than searching for a neutralizing agent. For products like bar soap, processed foods, or treated tap water, the sodium hydroxide has already been consumed or neutralized during production, so there’s no exposure risk from normal use.