Cysteine is a compound already found in hair, and it makes up about 40% of hair's natural protein composition. Cysteine hair treatment works to restore the proteins in hair that have been lost over time. It works in synergy with hair's existing proteins to restructure, soften, and release curls from hair. Unlike thermal straightening, with this therapy, there are more styling options. The curls and waves are merely smoothened not straightened. Besides, over time there is no demarcation line between the new growth and the treated hair.