CANADIAN ACADEMY The effects of cyclical bleaching on hair strength Vineet Chetan Yagnik IB Candidate Number: 000155-0038 2/12/2014 Word Count: 3,915 The research question of this extended essay is the following: “What are the effects of the number of bleaching cycles on the hair strength of female Asian hair?” Our experiment consisted of bleaching 27 hair switches for 1-3 cycles. The bleaching time ranged from 0 to 120 minutes, in 15 minute increments (Further information on this can be obtained in appendix A). We used a self-made method of measuring hair strength. Our method consisted of finding average hair diameter and the hair’s tensile strength, then dividing the tensile strength by the average hair diameter. We first bleached our switches then analyzed the hairs from the switches to see their hair strength. We hypothesized that a greater amount of bleaching cycles would result in lower hair strength. In conclusion, our data did not support our hypothesis. However, with further qualitative analysis of the hair, we found out that, qualitatively, our hypothesis was valid. Our data was inaccurate. This inaccuracy occurred possibly due to methodology errors and unforeseen shrinking in the hairs. For further research, we recommended to use a previously test method to evaluate hair strength—the 20 percent index—to reduce such errors and inaccuracies. Word Count: 195
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CANADIAN ACADEMY
The effects of cyclical bleaching on hair strength
Vineet Chetan Yagnik
IB Candidate Number: 000155-0038
2/12/2014
Word Count: 3,915
The research question of this extended essay is the following: “What are the effects of the number of
bleaching cycles on the hair strength of female Asian hair?” Our experiment consisted of bleaching 27
hair switches for 1-3 cycles. The bleaching time ranged from 0 to 120 minutes, in 15 minute increments
(Further information on this can be obtained in appendix A). We used a self-made method of measuring
hair strength. Our method consisted of finding average hair diameter and the hair’s tensile strength, then
dividing the tensile strength by the average hair diameter. We first bleached our switches then analyzed
the hairs from the switches to see their hair strength. We hypothesized that a greater amount of bleaching
cycles would result in lower hair strength. In conclusion, our data did not support our hypothesis.
However, with further qualitative analysis of the hair, we found out that, qualitatively, our hypothesis was
valid. Our data was inaccurate. This inaccuracy occurred possibly due to methodology errors and
unforeseen shrinking in the hairs. For further research, we recommended to use a previously test method
to evaluate hair strength—the 20 percent index—to reduce such errors and inaccuracies.
Word Count: 195
Vineet Chetan Yagnik IB Candidate Number: 000155-0038 February 12th, 2014 Word count: 3,915
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Table of Contents 0. Acknowledgements ................................................................................................................................... 3
4. Data ......................................................................................................................................................... 11
Raw data ............................................................................................................................................. 11
Processed data .................................................................................................................................... 11
Our data and our hypothesis ............................................................................................................... 13
Explanation of results ......................................................................................................................... 14
Qualitative evidence for hypothesis validity ....................................................................................... 14
Analysis of reliability and validity of our data.................................................................................... 15
T. Test .................................................................................................................................................. 15
Future improvements to ensure valid, reliable quantitative data ....................................................... 15
Storage of hair .................................................................................................................................... 16
More trials .......................................................................................................................................... 16
Vineet Chetan Yagnik IB Candidate Number: 000155-0038 February 12th, 2014 Word count: 3,915
7. Works Cited ............................................................................................................................................. 16
Works Cited ................................................................................................................................................. 16
Appendix A: Switch number and time+cycle information ...................................................................... 18
Appendix B: Raw data ............................................................................................................................. 19
Vineet Chetan Yagnik IB Candidate Number: 000155-0038 February 12th, 2014 Word count: 3,915
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0. Acknowledgements
Firstly, I would like to thank my dad for helping me so much throughout this extended essay. I
would also like to thank Mr. Dave Ferguson, my EE advisor and biology teacher, for his help and
feedback on the EE. I also thank Proctor and Gamble Japan for letting me borrow their resources and
their lab. This would not be possible without all of your help. Thank you very much!
Vineet Chetan Yagnik IB Candidate Number: 000155-0038 February 12th, 2014 Word count: 3,915
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1. Introduction
Focus
The research question and its significance
The research question of this extended essay is: “What are the effects of the number of bleaching cycles
on the hair strength of female Asian hair?”
This research is important as millions of people around the world bleach their hair. Statistics show that
almost 75% of women in America color their hair [1]. Coloring usually involves bleaching. With
widespread use of bleaching, it is important for us to understand the process of bleaching. Cyclical
bleaching is also popular. While significant research has been conducted on the effects of bleaching on
the human hair on hair strength, no research has been conducted on cyclical bleaching. We know effects
of a single cycle of bleach, however what are the effects of the second or third cycle?
The hair structure
Hairs have 3 main layers. [2] Figure 1.1 shows us a diagram of the layers of the human hair.
Figure 1.1: Cross section of human hair. Diagram obtained from [2]
The outermost layer of hair is called the
cuticle. It consists of overlapping ‘scales’ of
protein and lipids [3]. The cortex is the next
layer—it is the thickest hair layer and gives
the hair its color. The innermost layer is the
medulla. The medulla is the hollow center of
the hair. The cell membrane complex (CMC)
is the ‘glue’ of the hair and keeps all the
layers of the hair together [2]. The destruction of the CMC can result in the disintegration of the cuticle
[4].
The bleaching process
Bleach works by oxidizing a plethora of different compounds in the hair [5]. This results in the lightening
of hair that we desire. However, Wolfram et. al [6] showed that bleach also oxidizes the bonds in various
Vineet Chetan Yagnik IB Candidate Number: 000155-0038 February 12th, 2014 Word count: 3,915
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hair protein, rendering the proteins and affecting hair strength. Experiments have all shown such results—
more bleaching results in a decrease in hair strength [7] [8] [6].
Hair strength measurement and brief introduction on experiment method
We will generate data by bleaching various different hair switches for different times and different
bleaching cycles. We will then sample individual strands of hair and evaluate the hair strength.
We do not have the complicated materials required for more complicated methods, so we will use a self-
created method of hair strength measurement. Our method looks at tensile strength and the average hair
diameter. We divide the tensile strength by average hair diameter to get a relative value for hair strength,
with units g/µm. Our experiment will work by bleaching hairs for a range of times in 1-3 cycles and then
measuring the hair strength on said hairs.
Hypothesis
HNULL
There is no relation between the number of bleaching cycles and the hair strength of female Asian hair.
HALTERNATIVE
If we put hairs through a greater amount of bleaching cycles, the hair strength will decrease.
Explanation of alternative hypothesis
We know from past research that more bleaching time causes more hair damage [6-7]. Additional
bleaching cycles mean more bleaching time, resulting in a greater decrease in hair strength. In
addition, an extra bleaching cycle also means that bleach will need to repenetrate the hair with
every cycle.
To get inside the hair, bleach needs to pass through the cuticle. This requires the bleach to travel
through the CMC. Repeat entries through the CMC could possible result in complete damage of
the CMC, causing the cuticle to detach [4]. While the cuticle does not affect the structural
strength of hair [8], complete damage of the CMC does [4]. Not only that, as “self-repair is
impossible” [9] for hair, the CMC cannot regenerate.
Due to these various damage factors, I hypothesize more bleaching cycles will result in a greater