Thiolactic acid is the organosulfur compound with the formula CH₃CH(SH)CO₂H. The molecule contains both carboxylic acid and thiol functional groups. It is structurally related to lactic acid by the interchange of SH for OH. It is a colorless oil.

Thiolactic acid

Names
Preferred IUPAC name 2-Sulfanylpropanoic acid
Other names 2-Mercaptopropanoic acid
Identifiers
CAS Number	79-42-5 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:47872
ChemSpider	56121
ECHA InfoCard	100.001.097
EC Number	201-206-5
PubChem CID	62326
UNII	O5U6967KGF Y
CompTox Dashboard (EPA)	DTXSID80861636
InChI InChI=1S/C3H6O2S/c1-2(6)3(4)5/h2,6H,1H3,(H,4,5) Key: PMNLUUOXGOOLSP-UHFFFAOYSA-N
SMILES SC(C)C(O)=O
Properties
Chemical formula	C3H6O2S
Molar mass	106.14 g·mol−1
Density	1.22 g/cm3
Melting point	10 °C (50 °F; 283 K)
Related compounds
Related compounds	lactic acid, thioglycolic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Thiolactic acid was once widely used in hair permanent waving formulations, but has been displaced by formulations based on thioglycolic acid. Instead of using the acid itself, its salts are used. It is now mainly used for depilation.^[1]