Recently, the Center for Quantum Nanoscience of the Institute for Basic Science [IBS] swept the podium in related fields by inventing an atomic-scale storage medium. We are entering the 21st century nano age passing through the 20th century micro age.
The tiny and fine storage area, a discovery after a century of research, has already been planted on our heads. It is hair.
Hair starts growing even before birth. Seven weeks after conception, hair follicles1 are observed in the skin tissue. Around 10–13 weeks of pregnancy, the hair starts growing from the scalp, and around 20 weeks, eyebrows and eyelashes appear, and the fetus is covered by lanugo, a fine downy hair. Between 33 and 37 weeks, most of the lanugo falls out, and hair strands become thicker.
1. Hair follicle is a dermal tissue that surrounds the root of the hair and provides nutrition to hair.
Whether our hair is too much, too little, too long, or too short, we have plenty of concerns about it throughout our lives from the time when we are embryos. Why do we have hair, and what roles does it play? Let’s listen to the story a thin strand of hair has to tell us.
Giving Up on Hair and Protecting the Brain
Biologically, humans are classified as primates. One of the main characteristics that distinguish humans from other primates is that they don’t have noticeable hair on the skin. Although humans do have beard and head hair, their skin is definitely much smoother compared to chimpanzees or orangutans. What is the reason behind this?
Humans have larger brains relative to their body size than all other animals. Brain tissue is exceptionally sensitive to heat; heatstroke can occur when your body temperature reaches 104°F [40℃] and even a slight elevation of 2℃ can cause brain death. To avoid the life-threatening situation, the body must release heat before the core body temperature2 rises above normal. If humans had thick hair on their skin just like other primates, it would block the flow of heat and make it hard to control the body temperature.
2. Core body temperature is the temperature of blood in the heart and affects the brain tissue temperature.
Scientists assume that early humans had a lot of hair on their skin. Walking for just 10–20 minutes could lead to heatstroke, but only necessary hair remains on the human body now. Although the reason has not been clearly explained, it has helped humans keep their body temperature at 36.5℃ and protect the brain tissues.
The hair on the head, which is part of the remaining hair, covers the top of the human body, protecting the brain and the scalp from the outside world. When the head bumps into something, the hair serves as the body’s first line of defense. It provides a cushion to absorb impact, so that the brain will not be directly affected. Hair helps shield the scalp from the strong ultraviolet [UV] rays of the sun in summer, and it helps prevent heat loss to the outside air so that the body can endure the cold in winter.
Why Does Hair Fall Out?
Hair has been with mankind for a long time. However, it falls out helplessly. Sometimes a few strands of hair fall out, and sometimes even a handful of it falls out. It would be great if hair stayed the same forever, but how come it keeps falling out?
The primary reason why hair falls out is that each type of hair on the human body has its own lifespan. Just as a rose of sharon repeatedly blossoms and withers from the same tree, all hair including the hair on the head falls out after a certain period of time and grows back in the same place. These three repetitive phases—anagen, catagen, and telogen—are called the “hair cycle.” The hair’s growth phase lasts up to six years. On the contrary, other types of hair such as eyebrows, eyelashes, and lanugo have cycles less than six months, and they grow at half the speed of the hair on the head. This is the reason why they are a lot shorter than the hair on the head.
Hair follicle stem cells actively divide during the anagen phase of two to six years. Normally, hair grows about 0.4 mm per day, 1 cm per month, and 15 cm per year. However, lots of different factors affect the speed of hair growth, such as gender, age, ethnicity, health status, and season.
When the hair enters the catagen phase that lasts for several weeks, passing through the anagen phase, almost all hair cells die. It is followed by the production of new hair cells that generate new hair. During the telogen phase lasting for 4–6 months, the cell division stops and the hair falls out. The hair follicle takes a break, preparing to resume to the anagen phase.
Normally, 85% of our hair is in anagen and the remaining 15% in catagen or telogen. Many people let out a worried sigh when they see their hair fall out every morning, but considering that the average person’s head has about 100,000 strands of hair, it is normal to lose 50 to 100 strands of hair per day.
The Three Layers of Hair, Thin but Strong
The part of the hair above the scalp, which people typically think of when they hear the word “hair,” is called the hair shaft, and the rest of the hair, which is anchored in the follicle under the skin, is referred to as the hair root. The hair shaft has a diameter of typically 50–100 micrometers [μm],3 and it consists of three layers.
3. 1 micrometer is 1 millionth of a meter.
The hair shaft consists of the cuticle, cortex, and medulla. The medulla, the innermost layer of the hair shaft, is filled with air. The more air it contains, the shinier the hair looks. The medulla consists of irregular honeycomb-shaped cells, and it is normally found in thick hair.
The cortex, making up 80% of the hair, determines the hair’s elasticity, strength, texture, and color. The cells in the cortical form thick keratin filaments, giving the hair strength and flexibility. Eumelanin, a dark pigment, and pheomelanin, a lighter pigment, which affect the hair color, are also found in the cortex layer of the hair. Generally, Northeast Asians have more eumelanin, and North Europeans have more pheomelanin, which explains why hair color varies according to ethnicity. A reduced amount of melamin results in white hair, which is the original hair color. This happens to everybody, although the rate of hair graying differs from person to person.
The outermost layer is the cuticle which is 0.3–0.5 μm. Keratin-producing epidermal cells overlap like scales; they cover the inside of the hair and protect it from external stimuli such as heat, light, and chemicals. The epidermal cells face outward toward the end of the hair, which is to keep harmful insects from traveling up to the scalp. When you hold the hair and stroke it downward, it’s smooth, but it’s not so smooth when stroking it in the opposite direction.
This three-layer structure makes the hair strong although it looks thin. In the fairy tale “Rapunzel” by the Brothers Grimm, the witch and the prince climb to the top of the tower, holding Rapunzel’s long hair. This may sound like an absurd story from a fairy tale, but a strand of hair is stronger than we think. Of course, it may differ according to the thickness, damage, nutrient, and amount of moisture inside, but normally a strand of hair can support up to 150 g. Supposing that Rapunzel has 100,000 hairs, her hair can support up to 15 tonnes according to the theory.
Information from One Strand of Hair
These days, criminals are caught by their hair dropped at a crime scene, and blood relationship between a parent and a child is confirmed using hair, too. In fact, one strand of hair has so much information.
As the sequence of the DNA molecule chain differs from person to person, it can be used for identifying individuals, just like fingerprints. The hair root consisting of fossilized somatic cells have DNAs, too. Thus, it is possible to guess the owner’s gender, age, height, physical appearance, and even the disease the owner is likely to get, by extracting the DNA and analyzing the genes. With earlier techniques, it was only possible to separate mitochondrial DNA. However, humans have developed technology for separating nuclear DNA or genomic DNA, making it easy to extract meaningful DNA from hair.
When certain drugs are consumed, the drug ingredients are absorbed into hair roots through capillaries. Since the keratinized drugs move along the hair which grows from the hair roots, the intake of medication and the time of the intake can be found by testing the components depending on the length of the hair. There is also what is called Hair Tissue Mineral Analysis [HTMA] which evaluates the imbalance of nutrition inside the body, such as hypernutrition and nutrient deficiency, by comparing and analyzing the amount of some 30 minerals and 8 heavy metals inside the hair, and suggests the direction to take to maintain health.
Even without a thorough exam, health conditions can be guessed just by looking at the hair with the naked eyes. Hair is closely related to blood, because it grows by receiving nutrients from the blood that flows in the scalp. For humans who walk upright, sending the blood to the brain is harder than it is for other animals. For this reason, people who have anemia sometimes lose hair, because of a lack of nutrient supplied to the hair.
Hair repeats growing in the same spot during one’s entire life, protecting the scalp and giving a tremendous amount of information. The strength and the amount of information contained in such thin and fine space is beyond imagination.
“Do not be afraid of those who kill the body but cannot kill the soul. Rather, be afraid of the One who can destroy both soul and body in hell. Are not two sparrows sold for a penny? Yet not one of them will fall to the ground apart from the will of your Father. And even the very hairs of your head are all numbered. So don’t be afraid; you are worth more than many sparrows.”Mt 10:28–31
- Reference
- Park, Cheol-won. 탈모, 발모, 머리카락 세포 [Hair Loss, Hair Growth, Hair Cells]. Korea: Book Lab, 2013.
- Stenn, Kurt. Hair: A Human History. New York, NY: Pegasus Books, 2016.
- Lee, Hwa-yeong. 라푼젤도 모르는 머리카락의 비밀 [Secret of the Hair that Even Rapunzel Doesn’t Know]. Kids Donga Science Volume 5, March 1, 2011.