In recent years, a wide variety of cleaning agents have been used, causing various health problems. The main components of cleaning agents are surfactants, which have cleaning and emulsifying properties. While the health hazards of surfactants have been recognized empirically, they have been tolerated due to the perceived lack of alternatives.
1. Surfactants as a cause of scalp problems
◎Factors of hair thinning
One of the factors contributing to hair thinning is the aging of scalp and hair follicle cells, leading to increased hair loss or stunted hair growth. We discovered that surfactants used in shampoos and other products cause aging of scalp and hair follicle cells. This suggests that shampoos/treatments are one of the causes of hair thinning.
In addition to surfactants, cell damage caused by humectants, conditioning agents, preservatives, and base ingredients contained in shampoos/treatments cannot be ignored.
◎Structure of surfactants
General surfactants have two parts: a "hydrophobic group (fatty acid)" that is compatible with oil and a "hydrophilic group" that is compatible with water (Fig. 1).
This structure mixes substances that do not mix, such as water and oil, and washes away dirt from hair and scalp.
There are many types of surfactants. Depending on the differences in structure and properties, they are classified as follows:
2. Foaming power (lathering) and cleaning power
◎Principle of foaming power
Typically, surfactants form stable foams. This is because they reduce the surface tension of water. Hydrophobic groups align at the gas phase surface, and hydrophilic groups align at the water phase surface, stabilizing the foam structure (Fig. 2). Linear surfactants tend to form bubbles easily. When the hydrophilic groups are charged, they repel each other, increasing the stability of the foam.
◎Principle of cleaning
The cleaning power of surfactants depends on their ability to activate the interface between the solid phase (dirt) and the aqueous phase. Hydrophobic groups penetrate the dirt adhering to the skin and hair, and hydrophilic groups release the dirt (Fig. 3).
◎Measurement of cleaning power
We conducted cleaning power tests on typical surfactants and several commercially available shampoos. Oil was applied to a slide glass and placed in a surfactant solution. The solution was gently rotated, and the concentration of surfactant at which the oil completely disappeared in a fixed amount of time was measured. A stronger cleaning power corresponded to a lower concentration.
When comparing cleaning power and foaming power (lathering), the two did not correlate. In other words, the result was that lathering and dirt removal are not related.
3. Cytotoxicity Test
◎Test Method
Human fibroblasts or epidermal keratinocytes were seeded in petri dishes, and samples were applied for 30 minutes. After that, they were cultured in normal medium for 2 weeks, and the cells were stained blue (Fig. 4).
◎Test Results
Cytotoxicity tests were conducted on surfactants (over 100 types), conditioning & treatment ingredients (over 70 types), and shampoo & treatment products (over 50 types). Some of the test results are shown (Fig. 5).
◎Safe Surfactants
By analyzing approximately 150 types of hair care ingredients, we discovered surfactants with extremely low cytotoxicity. When compared by the concentration that reduces the number of colonies by half (ID50), the cytotoxicity was 100 times lower than that of commonly used surfactants (Fig. 5).
4. Mechanism of surfactant toxicity
◎Mechanism of cytotoxicity
We have researched the molecular mechanisms that cause the cytotoxicity of surfactants and have obtained the following results:
◎Characteristics of safe surfactants
General surfactants have hydrophilic and hydrophobic groups connected in a linear fashion (Fig. 6). While this structure provides excellent foaming power (lathering), it strongly binds to cell membranes and causes strong cytotoxicity.
On the other hand, surfactants with low cytotoxicity had large and complex hydrophilic groups. Polysorbates, a typical example, have a large steric structure. For this reason, they had poor foaming power and could not efficiently bind to cell membranes (Fig. 6). We believe this is why their cytotoxicity is low. 
5. Development of shampoo with low cytotoxicity
◎Design
We discovered a surfactant that is over 100 times less cytotoxic compared to commonly used surfactants. Using this, we developed a shampoo/treatment that is 100 times safer than commercial products in terms of cytotoxicity, and we have obtained a patent for it (Patent No. 7193108) (Fig. 7).
Additionally, all auxiliary ingredients used to improve feel and hair quality were analyzed, and high-performance ingredients that are as safe as possible were formulated.
◎Cytotoxicity and Skin Inflammation Tests
Commercially available shampoos and treatments invariably showed strong cytotoxicity. When applied to the skin, they also caused inflammation and inhibited hair formation.
It is believed that surfactants used in shampoos and similar products contribute to hair thinning by causing aging of scalp and hair follicle cells.
Therefore, after conducting cytotoxicity tests on approximately 100 types of surfactants, we discovered that surfactants widely used in shampoos and treatments, which provide good lather and strong treatment effects, have a significant adverse impact on hair-forming cells. Ultimately, it was "low-lathering surfactants" that had fewer adverse effects on the human body. This discovery enabled us to develop a shampoo that is ultimately gentle on the scalp.
We believe that the low-toxicity shampoo we developed has extremely low cytotoxicity and skin irritation, and can significantly improve scalp and hair problems. We aim to correct the unscientific belief in "lather" and promote safe and secure shampoos/treatments.
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