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Hair Science: Hair Structure 101 (With Diagrams)

She lives in tower because she had to sell the rest of the house to pay for conditioner.

She lives in tower because she had to sell the rest of the house to pay for conditioner.

Diagram of Hair Structure

Diagram showing the 3 major layers: Medulla, Cortex & Cuticle.

Diagram showing the 3 major layers: Medulla, Cortex & Cuticle.

How Human Hair is Structured

Let's take a look at the basic components of human hair structure. We'll break the structure up into the two major parts of a human hair: the shaft, or the part of the hair that's visible above the scalp, and the follicle, the part of the hair beneath the surface of the scalp.

The Hair Shaft

The entirety of the visible part of the hair that grows out of the scalp.

Cuticle- The visible part of the hair shaft. It is made up of flat, durable cells that overlap one another and act as scaled armor for the rest of the hair shaft. This protective layer is responsible for hair texture. When the cells of the cuticle are in their proper flattened position they can protect the vulnerable inner layers of the hair from weather and other damaging elements.

Cortex- The middle layer of the hair made up of tightly coiled strands of keratin, a dense and flexible protein. The keratin itself is composed of polypeptide chains of individual amino acid units. These amino acid units form a chain thanks to peptide bonds. Those chains then form even larger chains through polypeptide bonds.

  • Cortex bonds- There are 3 kinds of polypeptide bonds. Two of those bonds, salt and hydrogen, are physical and are broken and reformed on a regular basis. These bonds can be changed by temperature and moisture, among other external conditions the hair faces, and allow for the structure of the hair to be temporarily altered. Physical bonds are the reason you can straighten curly hair with a flat iron or rollers. The third type of bond is chemical and known as a disulphide bond. This chemical bond is much stronger and, unlike the two physical bonds, it is permanent. Only a chemical process can break and reform the disulphide bond.

Medulla- The innermost part of the hair. It is made up of tightly clustered cells that form a shaft through the very center of the hair. In some hair, the medulla is fragmented or absent altogether. Biologists do not yet fully understand the function of the medulla in human hair.

The Follicle

Located in the dermal layer of the skin, the hair follicle is where all the work is done. Stem cells regulate the production of hair within the follicle which is composed of the following parts:

The Root- Refers to the structures of the hair follicle in the dermal layer, beneath the visible, outer layer of the epidermis (the scalp).

  • Papillae- Dermal structures at the bottom of the hair follicle that provide oxygen and other nutrients to the hair via blood within their blood vessels. The papilla (singular) is made up of connective tissue that connects the hair to the scalp. If hair is pulled out, this is where the blood comes from.
  • Matrix- A bulb that almost completely surrounds the papilla. The cells produced in the hair matrix create the root sheath which gives hair its durability and structure. The cells within the matrix produce new hair through mitosis, or cellular division.
  • Bulb- The hair bulb simply refers to the bulbous structure of the hair follicle's base that sits within the dermis. It includes the papillae, the matrix and other types of cells that lend hair structure.

Inner Root Sheath- One of the first parts of the hair to develop, the inner root sheath shapes the rest of the hair and is composed of 3 layers:

  • Huxley's Layer
  • Henle's Layer
  • Cuticle

Outer Root Sheath- Has no role in hair production. The outer or external root sheath is tubular and empty, made up of epithelial cells.

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Human Hair at the Microscopic Level

Causes of Hair Damage

Now that we've covered the basics of human hair structure and function both above and below the scalp, let's look at some of the things that can cause damage to the hair:

  • Smog- If you live in a busy city like Los Angeles or New York, your hair is exposed to harmful pollutants day in and day out. This can cause a grimy buildup on hair that you may not even notice until the damage is done. Clarifying shampoos can help to strip away the buildup, but if you're not conditioning on a regular basis they can cause issues as well.
  • Humidity- We all know that warm climates can cause the dreaded frizzies, but many people don't know why. Humidity creates moisture in the air which causes a chemical reaction that opens the hair shaft. The moisture alters the hair's hydrogen bonds and causes the vulnerable middle layer of the hair shaft to break in places due to uneven water absorption.
  • Brushing- While it's true that 100 strokes a night leaves hair smooth and shiny, it can also cause damage and even frizz. While some frizz results from humidity, much of it is caused when the hair snags and breaks due to harsh brushing. Once the hair is broken, it will lay differently from the other healthy strands of hair and stick out, creating a frazzled look. It doesn't take a lot to break a hair shaft. If not done the right way with proper precautions, brushing can leave your hair more frizzy than tamed.
If your hair looked like this, you'd stare pensively at walls, too.

If your hair looked like this, you'd stare pensively at walls, too.

  • Heat Styling Tools- Flat irons and curling irons now come with heat settings that could cook a roast, so it's no surprise that heat is one of the most common causes of damaged hair.
  • Chemical Processing- Whether you dye your hair once every couple of months or use chemical straighteners on the regular, your hair is being damaged. Dyes, perms and other similar products work by interacting with the natural chemical processes within the hair to change its color, texture and sheen.
  • Shampoo- Most shampoos on the market contain harmful sulfates that strip hair of its natural oils in the interest of forming that soapy lather we all love so much. Even shampoos without sulfates are formulated to remove excess oils from hair and, no matter how good the ingredients list may be, there's no way to distinguish between good oil naturally produced by the body and bad.
  • Chlorine- Swimming can wreak havoc on even the healthiest tresses. Chlorine is a highly corrosive chemical that can change the texture and even color of hair in the event of prolonged exposure. Chlorine may be a threat found primarily in the summer months, but the damage it can cause lasts all year.
  • Hairstyles- The ways we choose to style our hair can cause as much damage as the products we use. Elastic bands can tangle and snag hair, causing it to break and resulting in even more frizz. Clips and pins may bend, rip and crimp delicate strands. Even wearing your hair in a style as simple as a ponytail can put strain on strands at the roots, affecting how they grow and even causing hair to fall out.
  • Diet- Consuming at least 5 fruits and veggies a day is a good idea for overall health, but hair is one of the first visible signs of what kind of diet we eat. Whether your diet is rich in nutrients or bereft of them, the first signs of any changes will show up in your hair and skin. A diet lacking in fats, oils, protein, antioxidants and other important, essential nutrients will result in dull, flat and lifeless hair.
Healthy hair must be stretched 70% before breakage occurs.

Healthy hair must be stretched 70% before breakage occurs.

Healthy Hair Strategies

Okay, so now you understand the basic structure of your hair and the major causes of damage, but how do you use that knowledge to prevent damage to the hair? Here are a few of the basic hair rescue strategies, each to be covered in-depth in future Hubs.

  • Limit the use of heat- When you flatiron or curl your hair, choose the lowest effective setting to avoid fried strands. Also, give hair a minimum of two days between the use of heated styling tools.
  • Choose styling tools carefully- Look for hair ties without metal fasteners, avoid any type of clip or hair fastener without silicon padding and choose a brush that's right for your hair type, for starters.
  • Guard hair against chemicals and heat with the right products- We all reach for the flatiron or a bottle of dye at some point, no matter how devoted we are to having healthy, lustrous locks. There are products out there that can minimize the damage.
  • Let hair dry naturally- Reserve blow drying for those times when you absolutely need to get ready in a hurry, even if it means changing the time you'd normally wash your hair to the evening instead of the hectic morning. Blow drying is an unnecessary source of damage to hair that can be (almost) completely eliminated with a little planning.
  • Use a clarifying shampoo- These shampoos get rid of the day's smog and any product residue your hair care regimen may leave behind. This leaves strands feeling fresh and clean and much more receptive to any treatments you may apply for moisture.
  • Condition, condition, condition- A good rule of thumb is to deep condition at least once a week and use a regular conditioner every time you wash.
  • Stop washing your hair every day- Not only does everyday washing actually increase oil production, but it can strip your hair of its natural oils, leaving it dry and prone to damage. A good dry shampoo can help for the 2-3 weeks it takes to detox hair from the effects of frequent washing.
  • Change your diet- Cutting out junk food isn't necessary to achieve vibrant and healthy hair. Dull and lifeless hair is almost always due to a lack of proper nutrients, so simply be aware of your daily intake of five fruits and veggies. Pay special attention to those high in antioxidants. Purple, dark green and red are the best go-to fruits and veg when in doubt.
  • Take a hair growth supplement- Biotin is one of the most effective supplements you can take for improving the health and appearance of keratin-based structures like hair and nails. Not only does it promote growth and shine but it fortifies hair and prevents breakage.
  • Massage your scalp- Too often we focus on the strands of hair themselves and not where they come from! Show your scalp some love for healthy, happy hair. There is some considerable evidence that a regular, gentle scalp massage can stimulate the stem cells that promote hair growth. Not only that, but it's a huge stress reliever. A friend or mate can do the job, but there are even products on the market designed specifically for scalp massage and hair growth.

Cool Facts About Hair

  • The average head of hair is made up of anywhere between 100,000-150,000 strands. That's a lot of hair!
  • Hair grows between 0.3-0.5mm per day.
  • Men's hair grows faster than women's. Isn't that a ripoff for both sexes?
  • Cutting or trimming hair doesn't actually make it grow faster. The hair you trim is dead and has no real effect on hair production at the follicular level, but it can make your tresses look shinier and feel healthier!
  • The average person loses around 100 hairs per day from brushing, washing and natural hair death.
  • Most dandruff shampoos do not actually affect the production of dandruff; they simply cover it with waxy buildup that makes hair dull.


lanablackmoor (author) from New England on September 29, 2016:

Great question! I try to avoid those shampoos that promise "smooth" hair and the like. You're right, they're usually full of waxy substances that only coat your hair. With enough buildup, the hair has a dull, lifeless appearance. Pantene is a major culprit of this, but Nexxus and most smoothing shampoos on the market are bad, too. I like to use a weekly DIY hair scrub made of 1 part baking soda to four parts water to remove all the waxy product buildup, followed by an apple cider vinegar rinse. It really helps remove all the crud from your hair, and I find that my other products can actually work when they're not competing with the buildup!

Yoleen Lucas from Big Island of Hawaii on September 29, 2016:

What do you think about conditioners that claim to strengthen fragile hair? A long time ago, Nexxus used to have one that coated the hair shaft with a wax - type substance, to keep it from breaking easily. I think it's still out there. Do you believe these are God to use?

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