Thioglycolate is a sulfur-containing chemical compound used primarily to break down hair. You encounter it most often as the active ingredient in depilatory creams (hair removal products) and in salon perming solutions. Different salt forms of thioglycolic acid serve different purposes: calcium thioglycolate dissolves unwanted body hair, while ammonium thioglycolate reshapes hair into curls or waves.
How Thioglycolate Works on Hair
Hair gets its strength from a protein called keratin, which is held together by sulfur bonds (called disulfide bonds). Thioglycolate breaks those bonds apart. When enough bonds are broken, the hair’s structure weakens dramatically. In a depilatory cream, this means the hair dissolves at the skin’s surface. In a perming solution, it means the hair becomes flexible enough to be reshaped.
The parent compound, thioglycolic acid, has the chemical formula HSCH2COOH. On its own it’s too harsh for direct use on skin, so manufacturers combine it with other elements to create salts that are more stable and easier to formulate into consumer products. The two most common forms are calcium thioglycolate (for hair removal) and ammonium thioglycolate (for perming).
Thioglycolate in Hair Removal Creams
Depilatory creams typically contain 5% to 6% calcium thioglycolate at a highly alkaline pH of around 12. That alkaline environment helps the thioglycolate penetrate the hair shaft and break down its sulfur bonds quickly. You apply the cream, wait five to 10 minutes, and then wipe or rinse it away along with the dissolved hair.
Timing matters. Leaving a depilatory on longer than the manufacturer recommends increases the risk of chemical burns, because the same chemistry that dissolves hair can also irritate skin. The product is designed to work within that narrow window, breaking down hair while the skin’s exposure stays brief enough to avoid damage.
Thioglycolate in Perming
Ammonium thioglycolate is the standard “perm salt” used in cold wave perming, a process that has been a salon staple for decades. The goal here isn’t to destroy the hair but to temporarily soften its internal structure so it can be reshaped.
The process works in two stages. First, hair is washed, wrapped around perm rods (the rod size determines how tight the curls will be), and then soaked in a solution of ammonium thioglycolate. The ammonia in the solution causes the hair to swell, letting the thioglycolate seep deep into each strand and break the disulfide bonds that hold the hair’s natural shape. At this point, the hair is flexible and takes on the curved shape of the rod.
Once the hair has been molded into the desired curl pattern, a second solution containing hydrogen peroxide is applied. This oxidizing step rebuilds the disulfide bonds in their new positions, locking the curl in place. Without this second step, the hair would simply return to its original shape once it dried.
Alkaline perms using ammonium thioglycolate typically operate at a pH between 9.0 and 9.6. They process without added heat, which is why they’re called “cold waves.” The trade-off is a strong, distinctive ammonia smell during the treatment.
Skin Reactions and Sensitivity
For most people, thioglycolate products used as directed don’t cause significant problems. A safety assessment of thioglycolic acid and its various salts found that clinically significant adverse reactions to these ingredients in depilatories are uncommon, and that current products are formulated to be practically nonirritating when used according to instructions.
That said, some people do develop allergic contact dermatitis from thioglycolate exposure. This is a delayed allergic reaction that typically shows up as redness, itching, or a rash on the skin that contacted the product. In documented cases involving ammonium thioglycolate at concentrations as low as 2%, allergic reactions persisted for more than 96 hours after a single exposure. Hairdressers are especially at risk because of repeated contact with perming solutions over years of work.
If you’ve never used a thioglycolate product before, doing a small patch test on a less sensitive area of skin (like the inside of your forearm) 24 hours before full application can help you spot a reaction before it becomes widespread. People who already know they’re sensitive to thioglycolate may need to explore alternative hair removal or styling methods entirely.
Other Uses of Thioglycolate
Outside of the beauty industry, sodium thioglycolate shows up in microbiology labs, where it’s a key ingredient in a liquid growth medium called thioglycolate broth. This medium is designed to grow bacteria that need little or no oxygen, making it a standard tool for identifying different types of bacterial infections. It works by scavenging oxygen from the surrounding liquid, creating a low-oxygen environment near the bottom of the test tube.
Various thioglycolate esters also appear in industrial applications, including as stabilizers in PVC plastics and as intermediates in pharmaceutical manufacturing. But for the vast majority of people searching this term, the connection to hair care products is the relevant one.