The Science Behind Hair Growth and Shedding Explained

Hair growth and shedding are natural processes that happen to everyone, yet many people find them mysterious or confusing. Why does hair grow in cycles? What causes hair to fall out? Understanding the science behind these questions can help you take better care of your hair and recognize when something might be wrong.

Hair is more than just a cosmetic feature. It plays roles in protection, sensation, and even social communication. This post will explain how hair grows, the phases involved, and why hair falls out. We will also explore factors that influence these processes and what you can do to support healthy hair.

Hair follicles in scalp skin tissue, showing hair growth process

How Hair Grows: The Hair Growth Cycle

Hair growth happens in a cycle made up of three main phases: anagen, catagen, and telogen. Each hair follicle on your scalp goes through these phases independently, which is why you don’t lose all your hair at once.

Anagen Phase: Active Growth

The anagen phase is when hair actively grows. It can last anywhere from 2 to 7 years depending on genetics, age, and health. During this phase, cells in the hair bulb divide rapidly, producing the hair shaft that extends out of the scalp.

• Hair grows about 1 centimeter per month during anagen.

• The length of this phase determines how long your hair can grow.

• Scalp hair has a longer anagen phase compared to body hair.

  
  

Catagen Phase: Transition

After the growth phase, hair enters the catagen phase, which lasts about 2 to 3 weeks. This is a short transitional period where hair growth stops.

• The hair follicle shrinks and detaches from the blood supply.

• The hair shaft becomes a club hair, meaning it is no longer growing but remains attached.

  
  

Telogen Phase: Resting and Shedding

The telogen phase lasts around 3 months. During this time, the hair follicle is inactive, and the club hair eventually falls out.

• About 10-15% of hairs on your scalp are in telogen at any time.

• New hair begins to grow underneath the resting hair, pushing it out.

• This natural shedding is why you lose about 50-100 hairs daily.

  
  

Why Hair Falls Out: Causes of Hair Shedding

Hair shedding is normal, but excessive hair loss can be concerning. Understanding why hair falls out helps distinguish between natural shedding and hair loss conditions.

Natural Shedding

• Hair naturally falls out at the end of the telogen phase.

• Seasonal changes, such as in autumn, can increase shedding temporarily.

• Stress or illness can push more hairs into telogen, causing noticeable shedding.

  
  

Androgenetic Alopecia (Pattern Hair Loss)

This is the most common cause of hair loss in both men and women. It is influenced by genetics and hormones.

• Hair follicles shrink over time, producing thinner and shorter hairs.

• Eventually, follicles stop producing visible hair.

• This type of hair loss usually follows a pattern: receding hairline or thinning crown in men, diffuse thinning in women.

  
  

Telogen Effluvium

This condition causes a large number of hairs to enter the telogen phase prematurely.

• Triggered by stress, surgery, illness, or medication.

• Hair shedding increases significantly but is usually temporary.

• Hair often regrows once the trigger resolves.

  
  

Other Causes

• Nutritional deficiencies (iron, zinc, vitamin D)

• Hormonal changes (pregnancy, menopause, thyroid disorders)

• Scalp infections or inflammation

• Certain hairstyles that pull on hair (traction alopecia)

  
  

The Role of Hair Follicles and Cells

Hair follicles are tiny organs in the skin responsible for producing hair. Each follicle contains several types of cells that work together to create hair.

• Matrix cells divide rapidly to form the hair shaft.

• Dermal papilla provides nutrients and signals to regulate growth.

• Melanocytes produce pigment that gives hair its color.

  
  

Damage or disruption to any of these components can affect hair growth and quality.

Factors That Influence Hair Growth and Loss

Several factors affect how hair grows and sheds. Understanding these can help you maintain healthy hair.

Genetics

Your genes largely determine hair thickness, growth rate, and susceptibility to hair loss.

Hormones

Hormones like androgens influence hair growth cycles. Changes during puberty, pregnancy, or menopause can alter hair patterns.

Nutrition

A balanced diet rich in protein, vitamins, and minerals supports hair follicle health.

Stress

Physical or emotional stress can disrupt the hair growth cycle, leading to increased shedding.

Hair Care Practices

Excessive heat, harsh chemicals, or tight hairstyles can damage hair and follicles.

Supporting Healthy Hair Growth

While some factors like genetics cannot be changed, you can support healthy hair growth through lifestyle and care.

• Eat a nutrient-rich diet including protein, iron, and vitamins A, C, D, and E.

• Manage stress through relaxation techniques or exercise.

• Avoid harsh treatments and minimize heat styling.

• Use gentle shampoos and conditioners suited for your hair type.

• Consult a healthcare provider if you notice sudden or excessive hair loss.

  
  

When to Seek Professional Help

If hair shedding increases dramatically or you notice bald patches, it is important to take action. At DuraStem we understand the science behind hair loss and regrowth. Our products are developed in our lab as a collaboration between doctors and scientists. We can help.