Hair bleaching

Howard Hughes' 1931 movie Platinum Blonde starring Jean Harlow is noted to have popularized platinum blonde hair color in the US. After the movie's success Hughes's team established a chain of "Platinum Blonde clubs" in several cities and offered a $10,000 prize that would go to any hairdresser who could copy Harlow's shade.[9] Though Harlow denied her hair was bleached,[10] the platinum blonde color was reportedly achieved with a weekly application of ammonia, Clorox bleach, and Lux soap flakes. This process weakened and damaged Harlow's naturally ash-blonde hair.[11]

During the 1930s Lawrence M. Gelb advanced the formulas of the bleaching products. In 1950, Clairol, the company Gelb founded with wife Jane Clair, introduced the first one-step hair dye product that lightened hair, which became a huge success with the masses.[9]

Melanin pigments, which give hair a darker color, can be broken down with oxidation.[12] Most commercial bleaching formulas contain hydrogen peroxide and persulfate salts, which under alkaline conditions created by ammonia or monoethanolamine can bleach the hair. Persulfate salts, in combination with hydrogen peroxide or alone, are known for their ability to degrade organics after activation with heat, transition metals, ultraviolet light, or other means that produce the sulfate radical. Without activation, the persulfate anion is known to react with some organic chemicals, although with slow kinetics.[13] When melanin is oxidized, oxygen gas is released.[12] Products for bleaching one's hair at home usually contain a 6% solution of hydrogen peroxide, while products for use in a hair salon can contain up to 9%.[12] Hair bleaching products can damage hair and cause severe burns to the scalp when applied incorrectly or left on too long.[14]

Industrial bleaches that work by reduction (such as sodium hydrosulphite) react with a chromophore, the part of the molecule responsible for its color and decrease the number of carbon-oxygen bonds in it, making it uncoloured. This process might be reversed to a certain extent by oxygen in the air, such as yellowing of bleached paper if left uncovered. In contrast, hydrogen peroxide chemically alters the chromophore by increasing the number of carbon-oxygen bonds. Due to the relative absence of reducing agents in the environment, chromophores cannot restore themselves as seen in reduction-based bleaches.[15]

Bleaching the hair is a gradual process and different colors may be achieved dependent on the original hair color, application time, and strength of the product used. Applied on black hair, the hair will change its color to brown, red, orange, orange-yellow, yellow, and finally pale yellow.[16]

Diagram showing which toner color should be used to counteract red, orange and yellow undertones in bleached hair.

Toning is a common practice after bleaching to mask the undesirable red and orange tones of "brassy" hair using a toner dye. Through toning, the yellow hue of fully bleached hair can be removed to achieve platinum blond hair. The appropriate color of the toner depends on the color of the bleached hair; e.g. to remove the yellow tones a violet toner dye will be needed, but to neutralize red and orange hues a green and blue toner would be more suitable. Tinted shampoos can also be used to tone hair.[16][17]

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[18] 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.[19]