Long hair

Long hair is a hairstyle where the head hair is allowed to grow to considerable length. Exactly what constitutes long hair can change from culture to culture, or even within cultures. For example, a woman with chin-length hair in some cultures may be said to have short hair, while a man with the same length of hair in some of the same cultures would be said to have long hair.

Males having short, cut hair are in many cultures viewed as being under society's control, such as while in the military or prison or as punishment for a crime, while males having long hair signify being outside of the mainstream. Long, thick hair has been a sign of wealth, power or prominence throughout time and history.

Long lustrous female hair is generally rated attractive by both men and women across cultures. The prevalence of trichophilia (hair partialism or fetishism) is 7% in the population, and very long hair is a common subject of devotion in this group.

Humans, horses, and orangutans are among the few species that may grow their head hair very long. Humans are believed to have lost their fur 2.5–3 million years ago as hominids when transitioning from a forest habitat to the open savanna, as an effect of natural selection, since this development made it possible to run fast and hunt animals close to the equator without getting overheated. An exception was however head hair, which was kept to provide thermal insulation of the scalp from the sun, to protect against ultra-violet radiation exposure, and also to provide cooling (when sweat evaporates from soaked hair). The ability to grow straight hair, has been observed among Homo sapiens sub-groups in less sunny regions further away from the equator. Relative to kinky Afro-textured hair, straight hair allows more UV light to pass to the scalp (which is essential for the production of vitamin D, that is important for bone development).

Scientists also view the ability to grow very long hair as a result of sexual selection, since long and healthy hair is a sign of fertility and youth. An evolutionary biology explanation for this attraction is that hair length and quality can act as a cue to youth and health, signifying a woman's reproductive potential. As hair grows slowly, long hair may reveal 2–3 years of a person's health status, nutrition, age and reproductive fitness. Malnutrition and deficiencies in minerals and vitamins due to starvation causes loss of hair or changes in hair color (e.g. dark hair turning reddish).

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