Mechanism of hair straightening

The document discussed the practice and theory of permanent hair straightening, noting that while it was commonly believed to require high pH with strong alkali, it could also be achieved at neutral pH with lithium salt or at acidic pH with resorcinol. The treatments varied in their effects on cystine, with some causing significant loss and others leaving it intact. Lanthionine production was also variable. The key requirement for effective hair straightening was the ability to induce supercontraction of the hair fiber.