Ammonium thioglycolate is a chemical used to straighten hair. Compared to other products, this chemical causes less damage to the scalp and hair, and the smell is not too strong. It works by making hair follicles more permeable and breaking down the disulfide bonds that make hair frizzy. This product is used as a step in a thermionic straightening system.

Compared to other chemicals that can be used in straighteners, ammonium thioglycolate is milder and therefore less damaging to hair. The mercaptan group of the chemical, -SH, makes it a reducing agent. This chemical gives an electron to another compound (chemical bond) to be broken down or reduced. There are many disulfide bonds in the hair. Very curly hair needs a lot of disulfide bonds, while straight hair needs a lot less. The ammonium in this compound causes the hair to expand, which then allows thioglycolate to enter the hair and reduce or break down disulfide bonds in the hair.

Removing ammonium thioglycolate requires thorough rinsing. Once the hair is styled and straightened, a hydrogen peroxide solution is applied. The hydrogen peroxide solution creates new bonds in the new hair. In general, the fewer bonds formed, the fewer curly strands. If this process is repeated too much, the hair will become weak and break easily.

Substituting this chemical for Guanidine Hydroxide or Sodium Hydroxide has many benefits. Ammonium thioglycolate has a lower pH, between 9-9.5, while sodium hydroxide has a pH as high as 14. Less alkaline chemicals do not damage the scalp or hair. Conditioning products are usually used before using hydroxide products, but ammonium thioglycolate is not required. In addition, this product does not have a strong odor when applied to hair. On the other hand, disulfide substances can smell bad, and other relaxation chemicals can produce a very strong pungent odor. Sulfides produced by thioglycolates convert sulfur into a non-volatile or non-odorant form of the chemical.

Bionic or thermionic systems also use this product to reduce the internal stress and structure of the hair strands. Hair is reconstructed with heat (normally perm) and then styled into a new straight look. Unlike other straightening products, the system sells well because straightening hair is very bright and soft.