In 2004, a Chinese woman named Xie Qiuping won the Guinness World Record for the longest human scalp hair at 5.627 meters—the length of an adult male giraffe! While this is an anomaly, humans are the only mammals that have negligible body hair, but extremely long hair on their heads. “It's such an important part of our identity as a species and yet, we understand so little about it,” said Maksim Plikus, a developmental biologist at University of California, Irvine, who studies the regeneration of hair.
In a paper published in the British Journal of Dermatology, Plikus and his colleagues—Nina Jablonski, an anthropologist at The Pennsylvania State University and Sung-Jan Lin, a dermatologist at the National Taiwan University—discuss why and how humans evolved this unique feature and speculate on the possible genetic mechanisms that drive the exuberant growth of these long and luscious locks.1
Three scientists, Sung-Jan Lin (left), Nina Jablonski (center) and Maksim Plikus (right) propose theories for the evolution of long scalp hair in humans.
Maksim Plikus, University of California, Irvine
Ancient Climate Challenges and the Role of Hair
One theory dates back to life millions of years ago, when human ancestors roamed across Africa, exposed to the blazing sun. As they spent a lot of time outdoors searching for food and water, they needed efficient mechanisms to keep their body cool. “In human evolution access to fresh water was always something that individuals and groups had to think about and plan over,” Jablonski said. “So having a thermoregulatory mechanism that would help to conserve precious water would be advantageous.” The absence of fur and abundance of sweat glands helped keep the body cool even after bouts of exercise, such as hunting animals.2 However, the head received the most solar radiation and probably needed other ways to keep it from overheating. Prehistoric cave paintings from Europe and Australia and Egyptian mummies with preserved hair suggest that long hair was a universal feature across different populations of humans.3,4
The Protective Power of Long, Curly Scalp Hair
Tightly curled and long scalp hair of ancient hominins could have evolved to shield the scalp from the sun, reduce heat transmission due to the air pockets between the curls and minimize water loss through sweat.5 While it is not known when curly hair emerged, it is likely that long hair growth evolved later to compensate for curly hair’s tendency for wear and tear.
Human Hair Growth Cycle and Length Potential
Hair length depends on the hair growth cycle. A hair follicle can either be in the active growth phase called anagen or the rest phase called catagen.6 Stimulatory signals trigger the proliferation of matrix cells in the hair follicle during anagen, lengthening the hair strand. A continuous supply of these cells is essential for the sustained growth of hair. A typical human scalp hair follicle stays in anagen for five to seven years, producing hair that is 50–110 centimeters (19–43 inches) long. For exceptionally long hair, such as that of Qiuping, the matrix cells would have to undergo over 11,000 divisions over more than 30 years!
“Hair follicle is like a biological 3D printer. Based on the molecular program you feed it, it'll print something tiny or something super long,” said Plikus. “You don't need to add any new components. You just have to instruct the various cells to work for longer and print for longer.”
The Genetics Behind Long Human Hair
Though no other mammal can boast of the exceptional hair lengths seen on human heads, the potential for long hair growth is conserved across the class, from the wispy “mustaches" of emperor tamarin monkeys to the meter-long body hair skirt of extinct Woolly mammoths. Studies on human dermatological conditions that alter hair length could provide insights on the molecular basis and genetic regulators of long scalp hair in humans. Mutations in fibroblast growth factor 5 (FGF5), a protein that promotes catagen entry, cause familial trichomegaly, a condition where body hair and eyelashes grow unnaturally long.7 Since the mutations prolong anagen throughout the body, it is likely that the gene is differentially controlled through modifications in its regulators in the scalp cells. Contrastingly, variants of the protein Wnt Family Member 10A shorten anagen, possibly causing conditions like androgenetic alopecia, or male pattern baldness.8
Toward Future Hair Growth Insights and Treatments
Scientists have started to dig deeper in the enigma of human scalp hair. Comparative studies of body and head hair using RNA sequencing and next-generation spatial sequencing, transplantation of human hair to rodent models, constructing computational models of hair growth and examining the intricacies of hair growth in individuals could unravel the molecular drivers of human hair growth. A clearer picture of how human scalp hair reaches considerable lengths could then lead to new therapeutic leads for conditions like hair loss or genetically stunted hair. “How could you treat a disease of short hair if you didn't even know what's the normal recipe for long hair?” Plikus pointed out.
Frequently Asked Questions (FAQs)
Q1: Why do humans have long hair on their heads but not on their bodies?
Humans evolved to have long scalp hair likely for thermoregulatory protection, while losing body hair to enhance cooling through sweat glands.
Q2: What is the biological reason behind long human hair growth?
Long hair growth results from an extended anagen phase in the hair cycle, where follicle matrix cells continuously divide to elongate the strand.
Q3: Are there genetic factors that determine hair length in humans?
Yes, genes such as FGF5 and WNT10A regulate the duration of the hair growth phase, impacting how long hair can grow.
Q4: Could understanding long hair growth lead to treatments for hair loss?
Definitely. Studying the molecular mechanisms behind long hair may uncover targets for therapies addressing conditions like alopecia.
- Chang LY, et al. Evolution of long scalp hair in humans. Br J Dermatol. 2025
- Ruxton GD, Wilkinson DM. Avoidance of overheating and selection for both hair loss and bipedality in hominins. PNAS. 2011;108(52):20965-20969.
- Finch D, et al. 12,000-Year-old Aboriginal rock art from the Kimberley region, Western Australia. Science Advances. 2020;6(6):eaay3922
- Ikram S. 1998. The mummy in ancient Egypt: Equipping the dead for eternity. London: Thames and Hudson.; 1998.
- Lasisi T, et al. Human scalp hair as a thermoregulatory adaptation. PNAS. 2023;120(24):e2301760120.
- Oh JW, et al. A guide to studying human hair follicle cycling in vivo. J Invest Dermatol. 2016;136(1):34-44.
- Higgins CA, et al. FGF5 is a crucial regulator of hair length in humans. PNAS. 2014;111(29):10648-10653.
- Cesarato N, et al. Short anagen hair syndrome: association with mono- and biallelic variants in WNT10A and a genetic overlap with male pattern hair loss. Br J Dermatol. 2023;189(6):741-749.
