Blue hair does not naturally occur in human hair pigmentation, although the hair of some animals (such as dog coats) is described as blue. Some humans are born with bluish-black hair (also known as "blue black" hair), which is black that has a blue hue under the light.
Fashion
The 18th-century English politician Charles Fox was a fashionable macaroni in his youth and tinted his hair with blue powder.
In 1913–1914, just before World War I, there was a vogue for dyed brightly-colored hair in different shades such as blue, violet or emerald. This started in Paris and then spread to other cities such as London. In 1924, the first celebrity hairstylist, Monsieur Antoine (Antoni Cierplikowski), dyed his dog's hair blue. An influential client, Lady Elsie De Wolfe Mendl, took up the same style and this started a new fad. Later in the 20th century, mature ladies had a blue rinse to conceal grey hair. The Queen Mother was the trend-setter and the peak of popularity for this fashion was the period following World War II.
In the 2007 fall fashion season, designers such as Marc Jacobs and Duckie Brown dyed the hair of their models blue to give them a shocking punk look. In 2011, the blue rinse became fashionable again and exemplars included Kate Bosworth with a dip-dyed style of turquoise tips while Thakoon Panichgul continued to present models with startling, all-blue hair.
A synthetic dye used to color hair blue was 1,4,5,8-tetraaminoanthraquinone prepared as Disperse Blue 1 with water and lignosulfonate dispersant. This is a semi-permanent dye as the dye molecules do not penetrate the hair shaft and so wash out in subsequent shampooing. It is not used in the U.S. as it is thought to be carcinogenic.
American politics
Beginning in the 2010s, and into the early 2020s, blue hair (and less commonly purple hair) has become associated with feminism, socialism, and the LGBTQ community, especially the young Generation Z and Millennial members of those socio-political movements. In response, supporters of conservatism in the United States and the Republican Party have started to use blue hair as a sign of an individual holding liberal philosophy. First coined by users of 4chan, itself often associated with the alt-right, conservatives in the US began using "blue-haired liberals" as a taunt towards who have "blue hair and pronouns".
Occupational causes
The hair of workers who regularly come into close contact with cobalt or indigo may become blue because of the dust of the substance mixing into the hair follicles. The colour in these cases is "not merely superficial."
Animals
Some varieties of rabbit have been bred with blue hair such as the Belgian breed, the Blue of Sint-Niklaas. This was a light sky blue in color with a white blaze. Other breeds of blue rabbit are darker and there are about 45 different shades or textures recognised by show judges.
There are several breeds of dogs which may have a blue coat including the Kerry Blue Terrier, Bluetick Coonhound and Grand Bleu de Gascogne. This arises in two main ways: from a dilution or silvering of a black coat so that it is seen as blue-grey; or from a mottling or marbling effect which mixes black and white to be seen as navy blue. Dogs with blue coats are often prone to skin allergies.
The fleece of sheep may be a natural blue-grey, such as the Himalayan blue sheep, or may be dyed blue as a raddle or to make them more conspicuous in snowy conditions.
Oxen breeds referred to as Blue Roane were plentiful centuries ago (shades of blue) and some of that genetics somehow evolved into slight tinting of blue in some Holstein cattle.
The coat of several other animals is called blue, including those of blue roan horses, the Russian Blue cat, and the blue variant of the Arctic fox's coat.
Artistic representations
Pictures
Blue hair has been described as a "sacred aesthetic" in ancient Egypt and Mesopotamia, where lapis lazuli was used in funerary art and statuary.
Many colored pictorials from the Anglo-Saxon tribes after the departure of Roman troops feature women with blue hair. According to Gale R. Owen-Crocker in Dress in Anglo-Saxon England "the use of colour in Anglo-Saxon art is not realistic ... and there is no need to assume dye was used on the hair."