The longest hair record in the world belongs to the Chinese Xie Qiuping, holder of the record since 8 May 2004, when her hair had an amazing length of 5.627 meters (18 feet and 5.54 inches).
Xie Qiuping, born in 1960, hasn't cut his hair since 1973; in the 31 years that have elapsed from that moment to the day of measurement, his hair has grown on average 18 centimeters per year, or 1.5 centimeters per month.
On average, a person's hair in the anagen phase (of growth) grows to around 1.25 cm a month; however, during their life cycle, the time comes when the hair prepares for the fall (catagen) to be replaced by new hair.
Generally, the growth phase lasts 2-4 years in men and 3-7 years in women, and in both sexes is influenced by hereditary factors; for example, look at random, it is longer in subjects of Asian race. Furthermore, the speed of hair growth is different in different areas of the head: the hair of the vertex region grows faster than those of the neck.
It should also be pointed out that even in the case of a sufficiently prolonged growth phase the length of the hair can be broken by external factors: tiling, permanent and environmental pollutants negatively affect the keratin that constitutes the hair shaft and, if this is particularly thin (characteristic determined genetically), will tend to break before having reached the maximum length guaranteed by the anagen phase.
