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Hair Elasticity: Unfolding the Science Behind Your Hair’s Stretchability

Table of Contents

Table of Contents

Image of curly girl who looks frustrated with her hair.

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Every day, millions of us wage war on our hair. We often pull, twist, heat, and style it without realizing the strain we’re putting on those delicate strands. Have you ever had your hair snap while trying to put it into a ponytail or noticed an increase in split ends? These are signs that your hair’s elasticity is suffering.

Hair elasticity is not just another buzzword in the beauty industry; it’s a crucial aspect of hair health, indicating how well your hair can withstand daily wear and tear. When your hair boasts good elasticity, it can stretch when wet and then bounce back to its original length without breaking – much like a perfectly tuned guitar string. But if it lacks elasticity, it may break under the slightest tension.

This article will explore the fundamentals of hair elasticity and its significance in determining hair quality. We’ll also discuss the factors that affect the elasticity of hair fibers, how hair loses its elasticity, and ways to treat or improve it. Additionally, I’ve reached out to my hair scientist friend, a Cosmetic Formulator holding a PhD in Chemistry, to provide expert insights for this information.

Understanding Hair Elasticity

Image of curly girl stretching some strands of hair.

Hair Structure and Elasticity

Hair, a protein fiber with a cylindrical structure, consists of microfibers neatly organized in the cortex. When force is applied to damp hair strands, it undergoes stretching due to the expansion of microfibers, functioning like springs within the hair cortex.

Vector illustration of the hair structure.

The Concept of Hair Elasticity

Experimental data indicates that untreated wet hair can stretch up to 30% of its original length, returning to its initial state upon drying. This phenomenon is termed hair elasticity.

Variability in Hair Elasticity

Elasticity levels vary based on ethnicity and hair type. Chemically treated or modified hair exhibits different elasticity compared to untreated hair, as it is influenced by the integrity of the tightly bonded microfibers in the hair cortex.

Impact of Chemical Treatments on Elasticity

Hair fibers with a well-packed and bonded cortex showcase high elasticity, while those with broken microfibers demonstrate reduced elasticity. Chemical treatments such as bleaching, processing, or exposure to UV damage contribute to decreased elasticity, often linked to the breakage of disulfide bonds in processed hair fibers.6,7 

Consequences of Excessive Force

Stretching hair beyond 30% through excessive force weakens its structure, leading to potential damage. Hair breakage may occur, measured experimentally as the “breakage load,” a crucial parameter determining the strength of a hair strand.

Hair Elasticity and Porosity

Image of hair cuticle showing low porosity, medium porosity, and high porosity.

When it comes to evaluating the mechanical strength of hair fibers, a crucial tool in the toolkit is elasticity. This term encapsulates the remarkable ability of hair fibers to revert or “bounce back” to their original shape or length after experiencing stretching or twisting.

In simple terms, elasticity gauges how resilient hair fibers are when subjected to force, determining their resistance to deformation. This concept is not just a casual consideration; it stands as a significant factor explored in scientific literature.1-4

The relationship between elasticity and porosity is direct and impactful.5 Hair fibers that boast good health and strength exhibit higher elasticity, showcasing the hair’s ability to withstand bending and return to its original state. Conversely, damaged hair fibers often display lower elasticity, indicating their susceptibility to shape deformation.

Elasticity: Stress, Strain, Young’s Modulus: Some Basic Terms

In physics, elasticity refers to a material’s ability to revert to its original shape after being subjected to stretching or misshaping by an applied force. This is determined by the ratio of stress (the amount of force per unit area) to strain (the extent of deformation, distance, or work done) resulting from the force.

Using hair fiber as an example, stress refers to the amount of force used to stretch the hair fiber, while strain describes the resulting increase in fiber length. The relationship between stress and strain is known as fiber elasticity.

The mathematical relationship defining these terms is given here:

E = Stress / Strain

E represents the elasticity, which is also known as Young’s modulus.

Measuring Elasticity

The elasticity measurement involves measuring the length increase resulting from an applied force. Mechanical analyzers can be used to measure both force and deformation in hair fibers.

Hair scientists use advanced technology like the Dynamic Mechanical Analyzer to the mechanical properties of a single hair fiber, including its strength, breakage load, and elasticity under specific humidity levels. Additionally, they use combing machines to assess the ease of combing and friction of both dry and wet hair fibers.

Ways to Test Hair Elasticity

You can easily test the elasticity of your hair yourself at home or at a salon with a professional.

At Home

Is it possible to check the elasticity of our hair at home? Yes, we can do a simple experiment to help us understand our hair fiber’s elasticity.

Put a mark on the scale of 30% and start stretching the hair fiber very gently by pulling it with your fingers. (Let’s say hair length was 10cm; its 30% would be 13cm). Stretch it to the 30% mark, hold it there for 10 seconds, and then release it. Let it come back to its original length and dry it out. 

  1. Grab a single hair strand and wet it with room-temperature tap water.
  2. Gently remove excess water with a paper towel.
  3. Place the hair strand on a sheet of paper and position a measuring tape alongside the side of the hair. Then, measure the length.
  4. Put a mark on the measuring tape at the 30% mark.
  5. Start stretching the hair strand gently by pulling it with your fingers. Stretch it to the 30% mark, and hold it there for 10 seconds.
  6. Then, release and allow it to return to its original length before drying it out.
  7. Let’s say your hair length was 10cm; its 30% would be 13cm. The hair should return to its original length; if it does not, it means you have low hair elasticity.

You may observe the following possibilities in this hair elasticity test:

● Your hair returns to its original state after completely drying, indicating that it is healthy and has good elasticity.

● Your hair doesn’t return to its original length when it dries; it may have low-to-medium elasticity.

● Hair breaks while being stretched, indicating that it is weak, damaged, indication low elasticity hair.

● You can estimate the elasticity of hair fibers by measuring the final length after the hair stretches and calculating the ratio between the normal state and the length after stretching.

At a Salon

If you want to check the elasticity of your hair at a professional level, then it is best to go to a salon for the assessment. Professionals can provide tips and products that are specifically designed to increase the elasticity of your hair.

They may use the following signs that indicate good hair elasticity:

Hair that can be stretched by up to 25–30% of its original length and then quickly returns to the same shape.

  • No breakage when combing or brushing.
  • No split ends, dry hair, or brittle strands.
  • A pleasant bounce and body in curly hair.
  • Shine.
  • Smooth cuticles.

If your hair feels a little rough, it means it needs moisture. On the other hand, if your hair is moisturized, it will have a smooth and silky texture. A combination of both —moisture and elasticity— is ideal for healthy hair.

Factors that Lower the Hair’s Elasticity

The elasticity of hair is closely tied to its structural integrity, consisting of two essential components: the outer cuticle layer and the inner cortex.

The cortex plays a pivotal role in providing mechanical strength to the hair. When either the cuticle layer or the cortex is damaged, it adversely impacts the overall structure, tensile strength, and elasticity of the hair. Several factors can contribute to damage, leading to a decrease in the fiber’s elasticity:

Physical Abrasion

Image of curly girl brushing her hair.

Excessive grooming, combing, brushing, and even heat styling can have detrimental effects on the structure of hair. This process initiates by causing damage to the outermost layer, known as the hair cuticle, and may eventually result in the removal of cuticles, exposing the inner layer called the cortex. Scientific research indicates that harsh brushing practices can lead to hair breakage.

Combing or brushing wet hair poses a challenge as wet hair tends to swell and be under osmotic pressure. Wet hair offers increased resistance, requiring more force during grooming, making it more susceptible to breakage. Numerous studies have highlighted wet hair fibers’ diminished elasticity and tensile strength.

Chemical Treatments

Image of girl receiving chemical processing of bleach.

Chemical treatments such as hair bleaching, perming, and relaxing can significantly impact hair fibers. For instance, hair bleaching often involves the use of alkaline hydrogen peroxide, leading to damage by oxidizing disulfide bonds and proteins. This results in a noticeable loss of strength and elasticity.

In the case of hair perming, alkaline thioglycolic acid is commonly used, while relaxing involves the application of sodium hydroxide or guanidine hydroxide. Both methods alter the chemical bonding in the hair structure, weakening the overall hair fiber.

Frequent use of these chemical treatments, leading to chemical damage, can eventually render the hair weak and prone to breakage during brushing or styling. These treatments weaken the hair, causing it to lose its natural elasticity. A protein treatment can help restore lost hair proteins, improving strength and elasticity.

UV Radiation

Image of curly girl with hair exposed to the sun.

When hair is exposed to UV radiation, it can cause the formation of free radicals (such as hydroxyl radicals) within the hair fiber. These free radicals can damage the protein structure of the keratin fiber and break down the chemical bonds within the hair, resulting in permanent damage. This can make the hair weaker, more brittle, and less elastic.

How to Recover or Improve Hair’s Elasticity

Maintaining hair elasticity is key for healthy, easily styled, and manageable hair. It becomes especially important after exposure to harsh chemical or physical treatments.

Consider incorporating specially formulated hair care products designed to strengthen the hair fiber to enhance or recover hair elasticity. Additionally, adopting a consistent and tailored hair care routine can contribute to the overall improvement of hair elasticity.

Here are some simple steps to help you regain the elasticity of your fiber:

1. Keep your hair clean and hygienic 

To prevent additional harm to the hair, it’s best to use a shampoo without sulfates. Sulfates are known to dissolve proteins from the hair shaft. 

2. Hydration

The moisture level is important for your hair’s health and quality. Hair that is dry and brittle tends to lose its elasticity and becomes tough, making it harder to manage and style. The best way to maintain a healthy water level of your hair fiber is to regularly use conditioning hair products such as conditioner, leave-in conditioner, and deep conditioner/hair masks.

3. Conditioning

Applying certain ingredients, such as cationic hair detanglers, conditioning polymers, and proteins, to the surface of hair can increase its elasticity. The polymers, in particular, create a thin layer over the hair and change its strength by penetrating the hair structure.

Protein treatments like hydrolyzed wheat protein work similarly by allowing small protein fragments to enter the hair surface and penetrate deep into the structure. This helps fill empty spaces in the cortex caused by chemical treatments, restoring the hair fiber’s mechanical strength and boosting its elasticity.8 Therefore, regular conditioning and deep conditioning treatments are crucial for maintaining the health of your hair.

4. Minimize the harm from daily hair combing and brushing

To make combing and brushing easier and protect the strength of your hair, use a combing detangler or leave-in conditioner that contains detangling agents, emollients, and hydrating ingredients.

Summary

Hair elasticity is a fundamental parameter in determining its strength, health, and quality. The higher the elasticity, the stronger the hair fibers, and vice versa.

An applied force is measured to observe the resulting stretch and increase in length to determine elasticity. Hair care labs routinely use this method to evaluate the mechanical strength of hair fibers and assess the level of hair damage.

Elasticity can be tested after using a conditioner to see if it has a beneficial effect on recovering or restoring elasticity to the hair.


References

1. Marsh, J. M.; Gray, J.; Tosti, A., Healthy Hair. Springer International Publishing: 2015.

2. Bhushan, B., Biophysics of Human Hair: Structural, Nanomechanical, and Nanotribological Studies. Springer Berlin Heidelberg: 2010.

3. Feughelman, M., The physical properties of alpha-keratin fibers. J Soc Cosmet Chem 1982, 33, 385-406.

4. Feughelman, M., Mechanical properties and structure of alpha-keratin fibres: wool, human hair, and related fibres. UNSW press: 1997.

5. Syed, A. N.; Ayoub, H., Correlating porosity and tensile strength of chemically modified hair. Cosmetics and toiletries 2002, 117 (11), 57-64.

6. Gao, T., Evaluation of hair humidity resistance/moisturization from hair elasticity. J. Cosmet. Sci. 2007, 58 (4), 393-404.

7. Wortmann, F. J.; Stapels, M.; Chandra, L., Humidity-dependent bending recovery and relaxation of human hair. J. Appl. Polym. Sci. 2009, 113 (5), 3336-3344.

8. Jachowicz, J.; McMullen, R., Mechanical analysis of elasticity and flexibility of virgin and polymer-treated hair fiber assemblies. J. Cosmet. Sci. 2002, 53 (6), 345-361.

HI,I'M VERNA

I’m just a girl who transformed her severely damaged hair into healthy hair. I adore the simplicity of a simple hair care routine, the richness of diverse textures, and the joy of sharing my journey from the comfort of my space.

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