Mechanism of hair straightening

Abstract

Synopsis The practice and theory of permanent hair straightening are discussed. Hair straightening as a cosmetic process is the reverse of hair waving. It removes hair curliness and makes wavy hair straight. While it is generally accepted that permanent hair straightening can be achieved only at very high pH with strong alkali, we have observed that it can also be achieved at neutral pH with lithium salt, or even at acidic pH with resorcinol. Also, while some of these treatments do result in considerable loss of cystine, others leave the cystine entirely intact. Lanthionine is produced in some cases, but is absent in others. It appears that the prime requirement for an effective hair straightening treatment is to be able to induce supercontraction of the hair fiber. Based on these observations, a model is proposed to explain permanent hair straightening in terms of certain molecular events such as chain folding and alpha-beta transformation of the polypeptide in the hair keratin.