Investigation on the effect of natural and synthetic shampoos on the tensile strength of hair

How does the tensile strength of hair depends on the percentage concentration and the type of shampoo (natural- Khadi Herbal Amla and Khadi Herbal Henna; synthetic – Tresemme and Sunsilk) it is exposed to, determined using a force sensor?

Use of cosmetics and the science behind them has always been a major topic of interest for me. Hair care and dermatology are one of the major sectors of the cosmetic industry across the globe and are also one of the major applications of chemical and biological science. When investigating hair products and shampoos, one comes across numerous conflicting researches and concepts, recent researches have debated the use of herbal alternatives instead of commercial synthetic products to be more conducive for the growth an strength of hair. Not only shampoo, but several other synthetic cosmetic products has been replaced by herbal formulations. These conflicting concepts have led me to conduct an experiment to investigate the effect on natural and synthetic shampoos on hair.

Hair comprised of natural oils and Keratin, which is a fibrous protein and the major constituent of hair shaft. It is synthesised by the cells in the cuticle of the germinal layer and has an alpha helix secondary structure. The ternary structure and quaternary structure of Keratin is mainly held in place by interactions such as the Hydrogen bonds, ionic interactions and disulphide linkages.

Apart from keratin, hair also contains elements like Ca, Cd, Cr and more along with some lipids. The minerals reach the hair follicles through blood circulation while the lipids are produced from the cells in the cortex. The minerals provide nutrition to hair while lipids make the hair fibre impermeable in nature and help in maintaining the force of cohesion between them. Sebaceous glands play a major role to maintain the quality of hair, they secrete mevalonic acid which condenses with fatty acids to produce sterols. The sterol and cholesterol together make a lipid film which is hydrophilic in nature. This lipid mixture helps to keep the hair shiny and silky. Excess of this lipid layer can give a greasy and dull appearance to hair while the lack of it makes it look dirty.

The quality of hair can be measured in terms of physical parameters like strength, tensile strength, elasticity and opaqueness. The tensile strength of hair is a major contributor to determine whether the hair is healthy and nourished or not. Since hair fibre has the property of elasticity, i.e the property of a material to return to its original shape or position after being stretched, it has naturally high tensile strength. However this strength can be affected by numerous factors such as nutrition, ageing, diet, applicants, conditioning and more.

Shampoo was first launched in the year 1930 under the name of the first shampoo product – ‘Drene’. History reveals that women in South Asian countries had a tradition to keep long hair. Soaps and in some cases even mud was used to cleanse dirt from hair. The problem detected was that soap can produce scum in the scalp especially if the water used is hard which is tough to rinse off.

The basic general composition of a shampoo contains:

• Synthetic detergents – both cationic and anionic. These are used to remove dirt from hair.
• Sequestering agents – Complexing reagents like EDTA, Vitamin-C which complexes with heavy metal ions in hair to remove them.
• Opacifiers – These compounds alter the physical texture and optical shine of hair. Thickeners are also added to control the viscosity of hair.
• pH adjusters – Hair shaft needs an optimum pH of 3.67. Shampoos are designed to maintain this pH. The pH of a shampoo must not exceed 5.5 as that would be harmful for scalp.

Apart from the above, conditioners, foaming agents and preservatives are also used.

Khadi Herbal Amla is a herbal shampoo which is composed of Amla, Reetha, Jatamansi, Bhringraj, Almond oil, and some essential oils. While the Khadi Herbal Henna shampoo contains Henna, Neem, Basil, Rosemary and Thorn apple. Tresemme is composed of surfactants like Dodecylsulfonate, sodium lauryl sulphate, Titanium oxide and EDTA along with other inorganic sequestering and odouring agents. Sunsilk is a product of Unilever mainly made of Sodium dodecyl sulphate, EDTA, dodecyl benzene sulphonate and amidopropyl betaine along with many other inorganic supplements.

This research’s aim was determining how natural (Khadi Amla & Khadi Henna) and synthetic shampoos (Tresemme & Sunsilk) effect the tensile strength of hair, along with investigating whether the concentration of shampoo also plays a role in affecting the tensile strength, and if there is a particular tolerance limit for shampoo or what the ideal recommended dose would be. This investigation will be carried out with the help of a force sensor to determine the breaking points of hair strands, In order to to determine the difference in tensile strength.

As synthetic shampoos contain a high number of artificial and damaging detergents which are not present in natural shampoos, it can be predicted that natural shampoos will improve the tensile strength of hair and hence hair strands exposed to natural shampoos will have higher tensile strength and higher breakage points.

As synthetic shampoos contain a high number of detergents which are not present in natural shampoos, it can be predicted that synthetic shampoos improve the tensile strength of hair due to the presence of such components. And so, the hair strands exposed to synthetic shampoos will have higher tensile strength and higher breakage points.

Results will show no or very little difference in the tensile strengths of hair strands, indicating that there is no difference between the effect of natural and synthetic shampoos on the tensile strength of hair strand.

Type of Shampoo (Natural and Synthetic) -

To be precise, the term natural here indicates that the shampoo claims to made out of ‘Ayurvedic’ or ‘Herbal’ formulations. Synthetic ones indicate that the shampoos are mainly based on synthetic detergents with inorganic components as sequestering or pacifying agents.

The natural shampoos chosen are Khadi Herbal Amla shampoo and Khadi Herbal Henna shampoo while the synthetic shampoos chosen are Tresemme & Sunsilk.

Percentage concentration of shampoo used -

The concentration of shampoos is varied to determine if there is a correlation between the quantity of shampoo and the resulted tensile strength of the hair strands. This will also address the common concept of  “using more shampoo for gaining better hair results” to determine whether it is true or a myth. The concentrations are 10.00%, 20.00%, 30.00%, 40.00% and 50.00%. All these concentrations were achieved by adding requisite amount of shampoo to tap water in a test tube. For example, to make a 10.00% shampoo solution, 1.00 cm³ of shampoo was added to 9.00 cm³ of tap water.

Tensile strength (measured using a force sensor)

The difference in the tensile strength of the hair strands, after being exposed to natural and synthetic shampoos of different concentration is measured to determine the effect of these shampoos and concentrations on hair.

• Protective clothing like lab coats, safety masks and safety gloves were used.
• Any consumable eateries were not allowed inside the laboratory.

• Hair samples were obtained from the same area of scalp and of the same source.
• All the hair strands were cut to a length of 10 cm. A ruler and a scissor were used for this.
• 80 such hair strands were made.

Determination of tensile strength of hair strands:

20 test tubes were taken. These test tubes were divided into five groups- 10%, 20%,30%,40% and 50% - each group having 4 test tubes. The composition of the test tubes are described in the table below:

In each of the test tube, five hair strands were transferred using a forcep. The test tube was covered with a filter paper and tied with a rubber band. After 24 hours, (same time on the next day), the hair strands were taken out. All the hair strands were then washed under a stream of running tap water. After washing, the hair strands were dried using a hair dryer. Then the hair strand was tied with a force sensor and the force sensor was secured at a wall. The force applied through the sensor was increased gradually using the screw and the force at which the hair strand breaks was recorded. The same process was performed for each and every hair strand.

The above graph is a scattered plot. It has a percentage concentration of the shampoo used along the x axes. The average tensile strength is the dependent variable of the investigation. Thus, it is plotted against the y axes. The dotted lines represents the trend lines as plotted using MS-Excel. The equation followed by the trend lines are also displayed in the graph.

As indicated in the graph, the tensile strength of the hair strand decreases from 28.64 g to 24.33 g as the concentration of Herbal Khadi Amla increases from 10.00% to 50.00%, the tensile strength of the hair strand decreases from 25.66 g to 22.43 g as the concentration of Herbal Khadi Henna increases from 10.00% to 50.00%, the tensile strength of the hair strand decreases from 18.91 g to 14.22 g as the concentration of Tresemme increases from 10.00% to 50.00%, the tensile strength of the hair strand decreases from 16.52 g to 12.14 g as the concentration of Sunsilk increases from 10.00% to 50.00%. In all four cases, the tensile strength decreases as the % concentration of the shampoo increases. It means that as the concentration of the shampoo the hair strand is exposed to increases, the tensile strength or in other words the quality of the hair strand decreases.

The trend line plotted follows linear equations. Comparing the gradients of the linear equations obtained, we can compare the extent to which the shampoo affects the tensile strength of the hair strand. The gradients of the linear equations as displayed in the graph are – 0.1116, 0.0875, 0.1131 and 0.1025 for Herbal Amla, Herbal Henna, Tresemme and Sunsilk respectively. As the magnitude of the gradient is maximum for Tresemme, it can be claimed that the decrease of tensile strength with the increase in percentage concentration of shampoo is most effective for Tresemme and least for Herbal Khadi Henna as it has the lowest magnitude of gradient.

The graph above is a bar graph. It compares the average values of tensile strength of the hair strand for various types of shampoo. The values are already displayed in the graph. As clearly indicated, the magnitude of tensile strength is higher for the natural or herbal shampoo like Khadi Amla and Khadi Henna while it is much lower for the synthetic ones like Tresemme and Sunsilk. It again confirms that hair has a much lower value of tensile strength in presence of synthetic shampoo instead of natural shampoo. Thus, natural shampoos will have much less harmful impact on the tensile strength of the hair strand in comparison to the synthetic shampoo.

Statistical analysis

The purpose of the statistical test is to assess if there is any significant difference between the way the type of the shampoo – natural or synthetic affects the way the percentage concentration of the shampoo changes the tensile strength of the hair strand.

Significance level (alpha) = 0.05

Number of values in Data Set-A (n_A) = 5

Number of values in Data Set-B (n_B) = 5

Degrees of freedom = n_A + n_B – 2 = 5 + 5 – 2 = 8

Critical value of t = 2.3060

\(\sum\)(A)² = (27.15 + 26.68 + 25.46 + 24.27 + 23.38)² = 16111.2249

\(\sum\)(B)² = (17.72 + 16.30 + 15.41 + 14.59 + 13.18)² = 5956.7524

Mean of data set-A = \(\frac{27.15+26.68+25.46+24.27+23.38}{5}\)  = 25.386

Mean of data set-B = \(\frac{17.72+16.30+15.41+14.59+13.18}{5}\) = 15.436

\(\sum\)(A²) = (27.15)²+(26.68)² +(25.46)²+(24.27)²+(23.38)² = 3232.8138

\(\sum\)(B²) = (17.72)²+(16.30)²+(15.41)²+(14.59)²+(13.18)² = 1203.737

Observed value of t = \(\frac{mean\ of \ Data\ Set\ A-mean\ of\ Data\ Set\ B}{\{\bigg[\bigg(\frac{(\sum(A^2)+\frac{\sum(A)^2}{n_A}}{n_A\ +\ n_B\ -\ 2}\bigg)+\bigg(\frac{(\sum(B^2)+\frac{\sum(B)^2}{n_B}}{n_A\ +\ n_B\ -\ 2}\bigg)\bigg][\frac{1}{n_A}+\frac{1}{n_B}]\}^\frac{1}{2}}\) = 9.52189

As the observed value (9.52189) is greater than the critical value ( 2.3060), thus the p value is less than 0.05. Hence, the null hypothesis must be rejected and the alternate hypothesis must be accepted. Thus, we can claim that there is a significant difference between the way the percentage concentration of the natural and the synthetic shampoo affects the tensile strength of the hair strand used.

How does the tensile strength of hair depends on the percentage concentration and the type of shampoo (natural- Khadi Herbal Amla and Khadi Herbal Henna; synthetic – Tresemme and Sunsilk) it is exposed to, determined using a force sensor?

Figure - 10 shows, as the concentration of the shampoo the hair strand is exposed to increases, the tensile strength or in other words the quality of the hair strand decreases. the tensile strength of the hair strand decreases from 28.64 g to 24.33 g as the concentration of Herbal Khadi Amla increases from 10.00% to 50.00%, the tensile strength of the hair strand decreases from 25.66 g to 22.43 g as the concentration of Herbal Khadi Henna increases from 10.00% to 50.00%, the tensile strength of the hair strand decreases from 18.91 g to 14.22 g as the concentration of Tresemme increases from 10.00% to 50.00%, the tensile strength of the hair strand decreases from 16.52 g to 12.14 g as the concentration of Sunsilk increases from 10.00% to 50.00%. In all four cases, the tensile strength decreases as the % concentration of the shampoo increases.

Comparison of magnitude of gradient of linear plots obtained in Fgure - 10 suggests decrease of tensile strength with the increase in percentage concentration of shampoo is most effective for Tresemme and least for Herbal Khadi Henna.

Figure - 11 again confirms that hair has a much lower value of tensile strength in presence of synthetic shampoo instead of natural shampoo. Thus, natural shampoos will have much less harmful impact on the tensile strength of the hair strand in comparison to the synthetic shampoo.

As revealed by statistical tests, there is a significant difference between the way the percentage concentration of the natural and the synthetic shampoo affects the tensile strength of the hair strand used.

• The procedure is adopted simple, easy and replicable.
• Low values of standard deviation, as reported in Figure - 5 to Figure - 8 confirms high accuracy of the data collected.
• The hair strands taken for the investigation were from the same origin and of same length. This reduces the possibility of sampling error in the investigation.
• To replicate the real life practices, the hair strands were washed with running stream of tap water and dried with a hair dryer before measuring the tensile strength and Tap water has been used instead of distilled water.
• Any significant anomalous data are not observed.
• The tensile strength of the hair strands has been measured using a force sensor. This is a digital apparatus which can read the mass that the hair can withstand till the precision of 0.01 g. Thus, the data collected is more reliable and less uncertain.

• In the raw data tables, Fgure - 5 to Figure - 8, it is noted that for the same percent concentration of the same shampoo, when the tensile strength has been measured for five different hair strands, the values are different (trial values of the same percent concentration and of same shampoo differs). Thus, it means that there is a random error leading to lack of precision in the investigation. To avoid this, the average values are considered instead of taking the individual values.
• Intrinsic variability is a systematic error of almost all biological investigations. This applies to this investigation as well. As hair strands are used, it must be noted that even if the hair strand are collected from the same source and preferably from the same area of the scalp yet the quality and biological composition index of one hair strand can still differ from the other. This will again lead to inaccuracy of the investigation conducted. To avoid this, artificially manufactured hair strands ensuring that the composition is unaltered can be used.
• Sample size also dictates the random error of an investigation. If the sample size is low, the impact of uncertainty on the result concluded is high and thus the result obtained is not reliable. This investigation deals with a sample size of five different percentage concentrations for each type of shampoo and five trials in each category of percentage concentration. Thus, in total (5×5) = 25 data points are collected for each type of shampoo leading to a large sample size and thereby reducing the random error of the investigation.
• As a force sensor was used to measure the tensile strength, the instrumental error associated with it will also impact the reliability of the conclusion. This introduces a systematic error in the investigation. To deal with this, the instrument used must be calibrated before operation.
• Disturbances or perturbation of the environment may also affect the reliability and precision of the data collected. Thus, all the test tube containing the hair strand immersed in the shampoo solutions were covered with a filter paper and a rubber band so that the external environment does not affect the subject under study. All test tubes were kept in the same place and all data were also collected on the same day.
• Experimenter’s fatigue is another possible source of random error. It is also described as human error in many cases. Collection of huge number of data being tedious may lead the experimenter to lose attention and incur an error while collecting the data. Thus, it is important to stay focussed or take certain occasional break while collecting the data. Moreover, the data must be collected in five different sets and average values must be considered to reduce the chances of human error.

Apart from using shampoo, another important cosmetic product for hair treatment is hair colour or bleach. These hair colours are dyes (nitrogenous aromatic compounds) dissolved either in ammoniacal solvent or in dry ether. These dyes are of two types- pigments extracted from various fruits or flowers; synthetic ones prepared artificially in the laboratory. The use of hair colour may also affect the quality of hair especially the hair colour that contains ammonia. I would like to repeat the same investigation using two main categories of hair colours – natural hair colours which are free from ammonia and synthetic ones that contains ammonia. The natural hair colours that may be used are – Khadi Herbal and Shahnaz Hussain Hair Colour while the commercial varieties that can be used are Loreal Paris and Salon Secret. I would like to make a paste of this dry powder of hair colour and apply it on the hair strand. Often hair stylist says that longer you apply the paste on your hair, better the colour your hair attains. Thus, I would vary the time the hair colour paste was applied on the hair strand and left to dry. After being dried, I would test the tensile strength of the coloured hairs in the same way. This would let me to understand how the time for which the hair color was applied on the hair strand and the type of hair colour used- natural or synthetic affects the tensile strength of the hair.

Ohyama, Manabu. “Hair Biology and Hair Loss Disorders: An Update and New Concepts.” The Journal of Dermatology, vol. 39, no. 1, 2011, pp. 2–2., doi:10.1111/j.1346-8138.2011.01479.x.

Tomorrow, Beauty. “The Chemical Properties of Hair.” Medium, Medium, 1 Apr. 2015, medium.com/@beautytmr/the-chemical-properties-of-hair-955985908d05.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4458934/