For centuries, a shining dome has been a symbol of intelligence, but despite this, many balding people still wish their hair would return. Scientists have long pondered, “Why do some people lose their hair, and how can we bring it back?

Hair Cycle

The full-headed among us have about 100,000 to 150,000 hairs on our scalps, and scientists have discovered two things about this dense thicket. Firstly, the sprouting hair we see is mostly made up of keratin, the protein leftover from dead cells that are forced upwards as new cells grow beneath them. Secondly, the structures that drive hair growth are called hair follicles, a network of complex organs that forms before we’re born, and grows hair in an everlasting cycle. This cycle has the following three main phases.

Anagen

The growth phase, which up to 90% of your hair follicles are experiencing right now, causing them to push up hair at a rate of one centimeter per month. Anagen can last for two to seven years, depending on your genes.

Catagen

After this productive period, signals within the skin instruct some follicles to enter a new phase known as catagen, or the regressing stage, causing hair follicles to shrink to a fraction of their original length. Catagen lasts for about two to three weeks and cuts the blood supply to the follicle, creating a club hair, meaning it’s ready to be shed.

Telogen

Finally, hairs enter the telogen, the resting phase, which lasts for ten to twelve weeks, and affects about 5-15% of your scalp follicles. During telogen, up to 200 club hairs can be shed in a day, which is quite normal. Then, the growth cycle begins anew.

But not all heads are hairy, and, in fact, some of them grow increasingly patchy over time in response to bodily changes. 95% of baldness in men can be attributed to male pattern baldness. Male pattern hair loss is caused by a combination of genetic, hormonal, and environmental factors. Your genes inherited from both your parents, determine your sensitivity to hormones called androgens, particularly one called dihydrotestosterone (DHT). In people with this condition, follicles become incredibly sensitive to the effects of dihydrotestosterone, a hormonal product made from testosterone. Dihydrotestosterone causes shrinkage in these overly sensitive follicles, making hair shorter and wispier. But loss isn’t sudden. It happens gradually, along a metric known as the Norwood Scale.

The Norwood scale has seven stages. Each stage measures the severity and pattern of hair loss.

  • Stage 1. No significant hair loss or recession of the hairline.
  • Stage 2. There is a slight recession of the hairline around the temples. This is also known as an adult or mature hairline.
  • Stage 3. The first signs of clinically significant balding appear. The hairline becomes deeply recessed at both temples, resembling an M, U, or V shape. The recessed spots are completely bare or sparsely covered in hair.
  • Stage 3 vertex. The hairline stays at stage 2, but there is significant hair loss on the top of the scalp (the vertex).
  • Stage 4. The hairline recession is more severe than in stage 2, and there is sparse hair or no hair on the vertex. The two areas of hair loss are separated by a band of hair that connects to the hair remaining on the sides of the scalp.
  • Stage 5. The two areas of hair loss are larger than in stage 4. They are still separated, but the band of hair between them is narrower and sparser.
  • Stage 6. The balding areas at the temples join with the balding area at the vertex. The band of hair across the top of the head is gone or sparse.
  • Stage 7. In the most severe stage of hair loss, only a band of hair going around the sides of the head remains. This hair is usually not dense and may be fine.
  • Norwood Class A. The class A variation of the Norwood scale is a slightly different and less common progression of hair loss. The main differences are that the hairline recedes back uniformly, without leaving an island of hair in the middle, and there is no bald area at the vertex. Instead, the hairline progresses directly from front to back.

Factors resulting Hair Loss

  • Family history (heredity). The most common cause of hair loss is a hereditary condition that happens with aging. This condition is called androgenic alopecia, male-pattern baldness, and female-pattern baldness. It usually occurs gradually and in predictable patterns — a receding hairline and bald spots in men and thinning hair along with the crown of the scalp in women.
  • Hormonal changes and medical conditions. A variety of conditions can cause permanent or temporary hair loss, including hormonal changes due to pregnancy, childbirth, menopause, and thyroid problems. Medical conditions include alopecia areata, which is immune system-related and causes patchy hair loss, scalp infections such as ringworm, and a hair-pulling disorder called trichotillomania.
  • Medications and supplements. Hair loss can be a side effect of certain drugs, such as those used for cancer, arthritis, depression, heart problems, gout, and high blood pressure.
  • Radiation therapy to the head. The hair may not grow back the same as it was before.
  • A very stressful event. Many people experience a general thinning of hair several months after a physical or emotional shock. This type of hair loss is temporary.
  • Hairstyles and treatments. Excessive hairstyling or hairstyles that pull your hair tight, such as pigtails or cornrows, can cause a type of hair loss called traction alopecia. Hot-oil hair treatments and permanents also can cause hair to fall out. If scarring occurs, hair loss could be permanent.

Treatments

Below the skin’s surface, the roots that give rise to our hair actually remain alive. Using this knowledge, scientists have developed drugs that shorten the resting phase and force follicles into anagen. Other drugs combat male pattern baldness by blocking the conversion of testosterone to DHT so that it doesn’t affect those sensitive follicles.

Stem cells also play a role in regulating the growth cycle, and so scientists are investigating whether they can manipulate the activity of these cells to encourage follicles to start producing hair again.

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