December 8, 2008

Sensory Irritation During Use of Hair Color Products:“Can This Unpleasant Feeling be Reduced?”
Mandom Corporation (Head Office: Osaka, President Executive Officer: Motonobu Nishimura, hereafter“Mandom”) is involved in investigating and reducing the sensory irritation that may be experienced when using haircolor products. As part of that research, we have researched the sensory irritation of the scalp during use of hair color
products, independently established a method for appropriately evaluating this feeling, and found that this sensory
irritation is caused by pH.
We plan to announce the results of this research at the Asian Society of Cosmetic Scientists (ASCS) Yokohama
Conference on March 2-4.

1. Research Background
Currently, the most widely used hair color products are dual-component oxidative hair dyes. These produce longlasting color, enable expression of a wide range of brightness and color tones, and are used by many individuals formany coloring purposes, such as fashion and gray hair coloring. The first component of this sort of oxidative hair dyecontains the dye and an alkaline agent, while the second component contains hydrogen peroxide; users mix the two
before use. The oxidative hair dyeing mechanism works as follows: hydrogen peroxide is decomposed under alkalineconditions to produce substances with strong oxidizing power, which further decompose the melanin in hair andsimultaneously oxidatively polymerize the dyes in the formulation. In addition to the decomposition of hydrogen
peroxide, the alkaline agent also swells the hair, making it easier for dye to permeate into its interior. These functions ofhydrogen peroxide and the alkaline agent make it possible to simultaneously achieve two important functions for haircoloring: hair decolorization and hair dyeing.
However, despite this superior functionality, oxidative hair dyes may, during use, cause discomfort througha tingling sensation. Rarely, they can cause skin sensory irritation and inflammation. Although this sensory irritation has
been attributed to alkaline agents, pH, and hydrogen peroxide, very few research reports on hair color-caused sensory
irritation have been made.
Thus, Mandom has conducted research in order to determine the effects of the putative causative agents of hair color
sensory irritation—pH and hydrogen peroxide—as well as the relationship between sensory irritation and hair lightening
power (decolorizing power).
2. The Effects of pH and Decolorizing Power on Sensory Irritation
It has long been believed that the stronger the decolorizing power of a hair color product, the more likely it is tocause sensory irritation. Thus, we conducted an experiment on hair decolorization and skin sensory irritation using asample containing ammonia and another sample containing ammonia and ammonium carbonate. As shown in Figure 1,
the results of our decolorizing experiment indicated that the sample with ammonium carbonate had greater decolorizing
Contactmandom corp.
Public Relations Div.
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URL: https://www.mandom.co.jp/en/-1-Greater decolorizing powerpower. Conversely, the results of our skin sensory irritation evaluation experiment indicated that the sample withammonium carbonate caused less sensory irritation (refer to Figure 2). We believe that this is caused by the lower pH of
the sample containing ammonium carbonate in comparison to the sample without the compound.

Ammonia

Ammonia+ ammonium

Figure 1: Differences in Decolorizing Power Caused by Alkaline Agents

Sensory irritation score∆E: Indicates degree of color change. Higher values are correlated with greater decolorizing power.

Degree of Sensory
Irritation

Score

Unbearable

3

Clearly perceivable

2

Faintly perceivable1

No irritation

0Time passed (min)Figure 2: Intensity of Sensory Irritation Produced by Samples with Differing Decolorizing Powers
Ammonia
Ammonia + ammonium carbonate

3. Effect of Hydrogen Peroxide on Sensory Irritation
Hydrogen peroxide, an ingredient in the second component of hair color products, is believed to greatly contribute tothe sensory irritation caused by hair color. Thus, in order to clarify the effect of hydrogen peroxide on this sensory
irritation, we conducted an experiment on skin sensory irritation using a sample containing 4% hydrogen peroxide and asample containing no hydrogen peroxide. As a result, we discovered that the sample without any hydrogen peroxide-2-

Sensory irritation scorecaused significant sensory irritation and the degree of this sensory irritation was identical to that of the sample containinghydrogen peroxide (Figure 3). Additionally, the sample that did not contain hydrogen peroxide caused subjects’ skin to
become red and experience a strong feeling of heat.
From these results, it is clear that sensory irritation during hair color treatment is not attributable to the strongoxidative power of hydrogen peroxide or attendant decolorizing power (or, only attributable to a negligible level).
Sensory irritation depends largely on pH; high pH compounds cause sensory irritation accompanied by a burning
sensation.

Time passed (min)Figure 3: Differences in Intensity of Sensory Irritation based on the Presence or Absence of Hydrogen
0% hydrogen peroxide
4% hydrogen peroxide4. Future Applications in Hair Color Products
We plan to continue this line of research at Mandom, striving to reduce sensory irritation and other unpleasantfeelings experienced during use of hair color treatment as much as possible and launch hair color products that can besafely and comfortably used by our consumers.
Finally, we would like to indicate that we expect our current research to lessen only sensory irritation associatedwith hair color use, not allergic reactions to hair color products. In order to prevent allergic reactions, the Japan HairColor Industry Association advises that “individuals who have experienced rashes due to hair dyes” and “individuals
who have felt sick after using hair dyes” avoid using hair color products. We publicize these guidelines on our hair color
products and have not changed our belief that these individuals should avoid using hair color products.
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