I once wrote major parts of these wikipedia articles, where we cite a number of scientific papers: en.wikipedia.org/wiki/Long_hair

and en.wikipedia.org/wiki/Hair_fetishism.

LONG HAIR

... 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. ... Scientists also view the [human] 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).

...

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.[5][need quotation to verify] 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.[6] 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).

Psychological significance

Anthropologists speculate that the functional significance of long head hair may be adornment, a by-product of secondary natural selection once other androgenic/somatic hair (body hair) had largely been lost. Another possibility is that long head hair is a result of Fisherian runaway sexual selection, where long lustrous hair is a visible marker for a healthy individual.

PARTIALISM

Partialism is sexual interest with an exclusive focus on a specific part of the body other than the genitals.

HAIR FETISHISM

... Many cultures regard a woman's hair to be erotic. For example, many Islamic women cover their hair in public, and display it only to their family and close friends. ... According to the New Testament, a christian women should cover her head while in a church or in prayer.

A hair fetishist may enjoy seeing or touching hair, pulling on or cutting the hair of another person. Besides enjoyment they may become sexually aroused from such activities. ...

Hair fetishism comes from a natural fascination with the species on the admiration of the coat, as its texture provides pleasurable sensations. An infant develops this kind of pleasure to feel the hair on his or her early life, manifesting as aggressive behavior that will drive to pull the hair of people with which it interacts.