Hair bleaching, is the practice of lightening the hair color mainly for cosmetic purposes using bleaching agents. Bleaching can be done alone, combined with a toner, or as a step for further hair coloring. The most common commercial bleaching agents in use are hydrogen peroxide and persulfate salts, but historically other agents such as sulfuric acid, wood ash, lye and hypochlorite bleach were used. Hair can also become bleached unintentionally, such as through sun exposure. History
During the early years of the Roman Empire, blond hair was associated with prostitutes. The preference changed to bleaching the hair blond when Greek culture, which practiced bleaching, reached Rome, and was reinforced when the legions that conquered Gaul returned with blond slaves. Sherrow also states that Roman women tried to lighten their hair, but the substances often caused hair loss, so they resorted to wigs made from the captives hair. The bleaching agent used by the Roman women was composed of a solution of ashes from burnt nuts or plants.Diodorus Siculus, a 1st century BC Greek historian, described in detail how Celtic people bleached their hair: "Their aspect is terrifying... They are very tall in stature, with rippling muscles under clear white skin. Their hair is blond, but not naturally so: they bleach it, to this day, artificially, washing it in lime and combing it back from their foreheads. They look like wood-demons, their hair thick and shaggy like a horses mane.
Sun exposure
Excessive exposure to the sun is the most common cause of structural damage of the hair shaft. Photochemical hair damage encompasses hair protein degradation and loss, as well as hair pigment deterioration Photobleaching is common among people with European ancestry. Around 72 percent of customers who agreed to be involved in a study and have European ancestry reported in a recent 23andMe research that the sun lightens their hair. The company also have identified 48 genetic markers that may influence hair photobleaching. Medical significance
Drug testing methods using hair samples are found to be disrupted by chemical hair treatments including bleaching. According to a 2019 study bleaching has caused strong chemical degradation on cannabinoids in hair, while permanent colorings in single applications had only negligible effects on cannabinoids. A 2021 study found similar results for methamphetamine concentrations in hair.Persulfate containing products may produce a variety of cutaneous and respiratory responses, such as allergic eczematous contact dermatitis, irritant dermatitis, localized edema, generalized urticaria, rhinitis, asthma, and syncope. References
Further reading
Robbins, Clarence R. (2006-05-26). Chemical and Physical Behavior of Human Hair. Springer Science & Business Media. ISBN 978-0-387-21695-9.