Lye in its common commercial form, a concentrated solution of sodium hydroxide (NaOH), registers a pH in the range of roughly 13 to 14. A 10 percent solution of solid lye dissolved in water typically lands around pH 13.6 to 13.7, placing it near the extreme alkaline end of the pH scale. That number shifts depending on concentration, temperature, and even what kind of lye you’re dealing with, because not all lye is the same chemical.
How Concentration Changes the Number
The pH scale runs from 0 to 14 in everyday use, with 7 as neutral. Each whole number represents a tenfold change in hydrogen ion activity, so pH 13 is ten times more alkaline than pH 12 and a hundred times more alkaline than pH 11. For lye, the more sodium hydroxide you dissolve in water, the higher the pH climbs. A dilute solution, say 1 percent, might sit around pH 12 to 13. A 10 percent solution of two different commercial solid lye products measured at pH 13.62 and 13.74 in laboratory testing.1The American Journal of Emergency Medicine. Alkalinity of non-industrial cleaning products and the likelihood of producing significant esophageal burns A lye solution produced during industrial pulp processing came in at pH 13.45, with sodium ions making up nearly 99 percent of the dissolved cations.2Journal of Environmental Chemical Engineering. Valorizing and detoxifying alkaline lime mud waste from pulp mills via the production of high activity lime and lye
At full saturation, around 50 percent by weight at room temperature, sodium hydroxide solutions push past pH 14. That sounds odd if you think of 14 as the top of the scale, but the 0–14 range is a practical convention, not an absolute ceiling. Concentrated strong bases can exceed it. In practice, though, most people encounter lye at concentrations where pH falls in the 13 to 14 window.
Sodium Hydroxide Versus Potassium Hydroxide
The word “lye” applies to two different chemicals depending on context. Sodium hydroxide (NaOH), sometimes called caustic soda, is the most common industrial and household form. Potassium hydroxide (KOH), called caustic potash, is the other. Both are strong bases that dissociate completely in water, so at the same molar concentration their pH values are essentially identical. The difference matters more for what you’re making with them than for how alkaline they are. Sodium hydroxide produces hard bar soap, while potassium hydroxide yields liquid soap. Historically, the lye people made at home by leaching water through wood ash was primarily potassium hydroxide, since wood ash is rich in potassium carbonate.
Wood Ash Lye Is a Different Animal
If you’ve ever read about traditional soapmaking, you’ve seen references to lye water made from hardwood ash. This homemade version is chemically quite different from a jar of commercial sodium hydroxide. It’s a dilute, impure solution of potassium carbonate and potassium hydroxide, and its pH can be far lower than commercial lye. One study that characterized lye extracted from hardwood sawdust ash found a pH of just 7.5, which is essentially neutral.3Journal of Engineering Sciences. Characterization of the Physicochemical Property of Lye-Extract from Wood Sawdust and Its Alternative Use in Soap-Making That’s orders of magnitude less alkaline than commercial lye’s pH of 13 or above.
The reason is straightforward. Wood ash lye contains relatively small amounts of hydroxide ions mixed with a lot of water and various dissolved minerals like calcium, magnesium, and iron. The potassium content in that study was only about 7.3 milligrams per liter, far too little to push the pH anywhere near what pure KOH or NaOH would produce.3Journal of Engineering Sciences. Characterization of the Physicochemical Property of Lye-Extract from Wood Sawdust and Its Alternative Use in Soap-Making Traditional soapmakers had to boil down their ash lye repeatedly to concentrate it enough to saponify fat, and even then the results were inconsistent compared to modern soapmaking with measured amounts of commercial NaOH.
Why a pH Above 13 Is Dangerous to Skin
The extreme alkalinity of concentrated lye makes it one of the most corrosive household chemicals. At pH 13 or above, sodium hydroxide attacks biological tissue through two mechanisms. It breaks apart fats through saponification, literally turning the lipids in your skin into soap. And it unravels proteins through a process called liquefactive denaturation, which dissolves tissue into a slippery, gel-like state rather than charring or hardening it the way an acid burn might.4Journal of Burn Care & Research. Alkalis and Skin
This is part of why alkali burns are often considered more dangerous than acid burns of comparable strength. Acids tend to cause coagulation necrosis, where the damaged tissue itself forms a barrier that slows further penetration. Alkali burns do the opposite: the liquefied tissue provides no barrier, so the chemical keeps working its way deeper. That soapy, slick feeling you get if lye solution touches your skin is actually your skin’s oils being saponified in real time. It’s a signal to flush immediately and thoroughly with water.
The danger scales with both pH and concentration. A splash of very dilute lye at pH 10 or 11 will irritate skin but can usually be rinsed away without lasting harm. A concentrated solution at pH 13.5 or above can cause full-thickness burns in minutes if not washed off. This is why commercial drain cleaners based on lye carry prominent warnings, and why anyone making soap at home should wear gloves and eye protection when handling the raw solution.
How Lye Loses Its pH Over Time
One of sodium hydroxide’s less obvious properties is that it gradually weakens just by sitting in contact with air. The culprit is carbon dioxide. NaOH reacts readily with COâ‚‚ to form sodium carbonate, and then sodium bicarbonate, both of which are far less alkaline. Researchers studying this reaction found that the process happens in two distinct stages: first the sodium hydroxide converts to sodium carbonate, and then the carbonate converts to sodium bicarbonate. The speed of the first stage depends strongly on how concentrated the NaOH solution is, while the second stage proceeds at a roughly constant rate regardless of concentration.5PubMed. Carbon dioxide capture capacity of sodium hydroxide aqueous solution
This has practical consequences. If you leave a container of lye solution open to the air for weeks, its pH will drift downward as sodium hydroxide converts to carbonate and bicarbonate. Soapmakers who mix their lye solution in advance sometimes find their batches don’t behave as expected because the effective alkalinity has dropped. Solid sodium hydroxide pellets or flakes also absorb both moisture and COâ‚‚ from the air, which is why they come in airtight containers and why old, poorly stored lye may be weaker than the label suggests. Keeping lye sealed and using it relatively promptly matters for both safety and effectiveness.
This same COâ‚‚ reaction is actually exploited on purpose in some industrial settings. Sodium hydroxide solutions are used as a COâ‚‚ scrubbing agent in gas processing, precisely because the reaction is so efficient.5PubMed. Carbon dioxide capture capacity of sodium hydroxide aqueous solution What’s a nuisance for shelf life turns out to be a feature for carbon capture.
Where Lye’s pH Sits Among Common Household Chemicals
It helps to put lye’s pH into context by comparing it to other alkaline substances you might encounter. Baking soda dissolved in water has a pH around 8.3 to 8.5. Household ammonia typically runs around 11 to 12. Bleach (sodium hypochlorite at household concentrations) falls in the 11 to 13 range. Lye, at pH 13 to 14 in typical working concentrations, sits above all of these. The only common household chemicals that reach comparable pH levels are certain oven cleaners and heavy-duty drain openers, many of which contain sodium hydroxide as their active ingredient.
A study that tested the pH of various non-industrial cleaning products found that solid lye-based products, when dissolved to 10 percent concentration, were consistently among the most alkaline substances available to consumers.1The American Journal of Emergency Medicine. Alkalinity of non-industrial cleaning products and the likelihood of producing significant esophageal burns That same study was motivated by the clinical concern about esophageal burns from accidental ingestion, which underscores how seriously the medical community takes the pH levels lye can reach.
Food-Grade Uses and the pH Paradox
Given everything above, it surprises many people to learn that lye is a common food-processing ingredient. Pretzels get their distinctive brown, glossy crust from a brief dip in a dilute lye bath before baking. Olives are often cured in sodium hydroxide solution to remove their bitterness. Lutefisk, the Scandinavian preserved fish, is soaked in lye for days. Bagels, some noodles, and hominy all involve lye at some point in their preparation.
The key is concentration and exposure. A food-grade lye dip for pretzels uses a solution around 3 to 4 percent NaOH, which has a pH around 13 but is far less concentrated than the solutions used for drain cleaning. More importantly, the food spends only seconds to minutes in the bath and then gets rinsed, neutralized by other ingredients, or transformed by high-temperature baking. The residual alkalinity in the finished food is negligible. Your pretzel does not have a pH of 13 by the time you eat it.
In traditional food preparation around the world, similar alkaline treatments show up repeatedly. Nixtamalization of corn in Mesoamerican cooking uses calcium hydroxide (slaked lime) rather than sodium hydroxide, but the principle is the same: a strongly alkaline solution modifies the food’s texture and nutritional availability, then gets rinsed away. The pH of the treatment solution is high, but the pH of the final product is not.
Lye in Water Treatment and the Environment
Sodium hydroxide is widely used to adjust pH in water and wastewater treatment. Municipal water systems add small amounts to raise the pH of acidic source water, which helps prevent pipe corrosion and reduces lead leaching. In these applications, the goal is to nudge the water’s pH up to around 7.5 to 8.5, nowhere near lye’s full-strength alkalinity.
A more aggressive use appears in ballast water treatment for ships. Ballast water can carry invasive species between ports, and one treatment strategy involves spiking the water with sodium hydroxide to raise its pH above 11.5, a level lethal to most aquatic organisms. After treatment, the pH is brought back down before discharge by bubbling COâ‚‚-containing exhaust gas through the water, the same reaction that degrades lye on the shelf. Testing of this system showed that the treated water’s pH could be reduced to the 7.5 to 8.2 range, and that at those levels there was little to no residual toxicity to test organisms like water fleas and fathead minnows. Amphipods were more sensitive, but diluting the treated water by half and maintaining a neutral pH eliminated the toxic effect.6PubMed. An evaluation of the residual toxicity and chemistry of a sodium hydroxide-based ballast water treatment system for freshwater ships
The environmental picture with lye is that the chemical itself doesn’t persist. Unlike some pollutants that accumulate in sediments or organisms, sodium hydroxide reacts with COâ‚‚ in the atmosphere and with acids in the water, neutralizing itself over time. The concern is more about local, short-term pH spikes. Dumping concentrated lye into a stream would be catastrophic to organisms in the immediate area, but the alkalinity dissipates as it dilutes and reacts. The real environmental risks from lye releases tend to come not from the sodium hydroxide itself but from contaminants dissolved along with it, like copper in the ballast water system study.6PubMed. An evaluation of the residual toxicity and chemistry of a sodium hydroxide-based ballast water treatment system for freshwater ships
Measuring Lye’s pH at Home
If you make soap, cure olives, or use lye for any DIY project, you may want to check the pH of your solution. Standard litmus paper and most pH test strips top out at 14 and give poor resolution above pH 12, so they’ll tell you “very alkaline” but not much more. Liquid indicator drops have similar limitations at the extreme ends of the scale. A digital pH meter gives more useful readings, but you need one rated for high-alkalinity solutions. Cheap meters designed for aquarium or pool testing often max out around pH 12 and can be damaged by concentrated NaOH.
For soapmakers specifically, pH testing of the finished soap matters more than testing the raw lye. A properly cured bar of cold-process soap should have a pH around 9 to 10, mildly alkaline but well below the corrosive range. If your finished soap tests above 10 or 11, it may contain unreacted lye and could irritate skin. A simple tongue test (traditional but not recommended for obvious reasons) or a phenolphthalein indicator gives a rough check, but a pH meter is the reliable option.
Industrial Uses That Rely on Extreme pH
Beyond soapmaking and food processing, lye’s extreme alkalinity makes it indispensable in a range of industries. Paper and pulp manufacturing uses enormous quantities of sodium hydroxide to break down lignin, the compound that holds wood fibers together. The kraft process, which produces the majority of the world’s chemical pulp, relies on a solution of NaOH and sodium sulfide at high temperature and high pH. The lye produced as a byproduct in some pulp mill operations, with a measured pH of 13.45, gives a sense of the alkalinity involved in these industrial streams.2Journal of Environmental Chemical Engineering. Valorizing and detoxifying alkaline lime mud waste from pulp mills via the production of high activity lime and lye
Petroleum refining uses lye to remove sulfur compounds from fuels. Textile manufacturing uses it to mercerize cotton, a treatment that swells the fibers and gives them a lustrous finish. Aluminum production depends on lye to dissolve alumina from bauxite ore in the Bayer process. In each case, it’s the extreme pH that does the work, breaking chemical bonds and dissolving materials that resist milder treatments. The sheer volume of NaOH produced globally, tens of millions of metric tons annually, reflects how many industrial processes depend on having a cheap, reliable source of very high pH.
Hydrogen generation is another area where lye’s chemistry proves useful. Sodium hydroxide solutions can serve as the reaction medium when aluminum reacts with water to release hydrogen gas, a process being explored as a way to produce hydrogen on demand for portable fuel cells and remote power systems.7International Journal of Hydrogen Energy. Development and demonstration of a deployable apparatus for generating hydrogen from the hydrolysis of aluminum via sodium hydroxide The NaOH accelerates the reaction and prevents the aluminum from forming a passivation layer that would otherwise stop the process.