By Cleber Barros
Did you know that the pH of shampoos could have a big impact on product performance? Keep reading to learn how the pH of shampoos directly impacts the appearance of hair!
Shampoos are one of the best-selling cosmetic types in the world, since people need, almost daily, to wash their hair. However, shampoos are not only scalp cleaners: they also act on the hair strands, interfering in factors like brightness, frizz, combability, etc.
Among many factors that influence the final result, we have the concentration and quality of the surfactants, the addition to antistatic and lubricating agents and the final pH of the formulation. In this article, I will address a little bit about each of these factors.
Surfactants are molecules with hydrophilic and hydrophobic portions. Their hydrophobic area binds to the fats (tallow) and water-insoluble residue present in the hair, while their hydrophilic portion binds to the water, thus removing any residue from the hair and carrying it away.
When surfactants enter into contact with water, micelles form: surfactant molecules form a ring structure with the hydrophilic portion facing outwards and the hydrophobic portion pointing inside. Micellisation allows shampoos to bind strongly to the fat of the hair, but also to the water, allowing a complete cleaning of the hair, as all the dirtiness is washed away.
Depending on their electric charge, surfactants can be classified into four groups: anionic, cationic, amphoteric and non-ionic. The main surfactants used in cleaning systems are anionic (which have negative charges). Some examples of this kind of surfactant are sodium lauryl sulfate, ammonium lauryl sulfate, and sodium lauryl ether sulfate; the latter is used most widely.
Cationic, amphoteric and non-ionic surfactants are added to some shampoo formulations to reduce static electricity and possible irritant properties – effects which are generated by anionic surfactants. Because they are positively charged, cationic surfactants bind rapidly to the negative charges left on hair strands by anionic surfactants, reducing frizz.
In addition, such surfactants also optimize foaming and the final viscosity of the product. The static electricity verified after the use of shampoos is the result of the balance between positive and negative charges during the removal of sebum and waste. The negative charge of the capillary fibers repels the equally negative charges of the micelles. The repulsion allows water rinsability.
However, the pre-existing negativity of the strands increases, and stable complexes that bind to keratin also form. The excessive static electricity creates a repulsion between the strands. Although cationic agents try to neutralize this effect, the pH of the shampoo generates significant interference, which can increase electrical charges and reduce neutralization.
pH: Definition and importance
The pH indicates the acidity, alkalinity or neutrality of a given medium. The pH scale ranges from 1 to 14. Acidic substances have a pH lower than 7.0, 7.0 is neutral, and alkaline substances have a pH higher than 7.0.
The pH at which a protein or particle has an equivalent number of positive and negative charges is called the isoionic point, whereas the point at which a protein or particle does not migrate in an electric field is called an isoelectric point.
The isoelectric point of hair is around pH 3.67, while its isoionic point is around pH 5.6. Hair reaches ionic neutrality when the pH is near the isoelectric point. In bleached hair, the isoelectric point is reached at even lower pHs.
Free lipids containing fatty acids are an essential component of the hair surface,as they allow the absorption of surfactants and other ingredients. The longer the interval between shampoos, the more free lipids will accumulate and the lower the isoelectric point of the hair.
Any product applied on hair that has pH higher than 3.67 increases the static electricity and the repulsion between strands. The surface of the capillary fibers has a negative charge because of its low isoelectric point.
Water has a pH around 7.0. Therefore, when hair is rinsed, the negativity of the fibers increases and the negatively charged fibers repel (wash) the micelles . The negative electrical charge makes it difficult to comb, thus causing a frizz effect.
In addition, at an alkaline pH, hair has an increased ability to absorb water. The water penetrates the open cuticles, hydrating the fibers and breaking the hydrogen bonds of the keratin molecules. Keratin is a helix-shaped spiral molecule that remains in this shape due to the chemical bonds between its hydrogens, disulfides, ionic bonds and Van der Waals forces.
Water causes hydrolysis: it temporarily breaks the hydrogen bonds and makes the keratin molecule malleable. Consequently, the decrease in elasticity and increase in plasticity makes capillary fibers fragile.Thus, wet hair, when deformed, does not return to its original format. When the hair is wet, the cuticle scales lift, leading to fragmentation and breakage in the fiber shaft.
The pH of the scalp, however, is around 5.5, such as the other parts of the skin, which is more alkaline than the hair strands.
A study conducted with 123 shampoos of internationally traded brands, purchased in the city of Rio de Janeiro, verified that most of the products possessed a final pH higher than the pH of the hair strands (even higher than the pH of the scalp). There is no standard that determines the pH of shampoos, whether commercial/popular, antidandruff or dermatological shampoos (commercialized under medical prescription).
It is not mandatory that the pH range is indicated on the label or specified in product formulation. However, such a scenario is not observed in the products for professional use in beauty salons, where 75 percent of the products have a pH range within the optimal range of 5.5 or lower. According to current literature, the use of shampoos with pH higher than 5.5 can increase the friction of the hair, which leads to frizz, hair breakage and general hair unmanageability.
After using a shampoo, it is important to use a conditioning product, to restore some of the hair’s natural oiliness, as well as neutralize electrostatic forces caused by cationic surfactants). Conditioner helps eliminate frizz and seal capillary cuticles.
Dermatologists often do not recommend use of conditioners, so it is important to add cationic and lubricating agents to shampoo formulations. These ingredients will provide the ideal hair conditions.
However, the situation becomes different when we analyse infant capillary products, since the irritation of children’s eyes is a great concern. It is therefore necessary that the pH of infant shampoos be close to the physiological pH, between 6.0 and 7.0. Due to the higher pH range, it is important to remember that the use of children’s shampoos is not recommended for adults (especially those with colored hair).
Shampoos with pH above 3.67 often contain cationic agents to reduce electrostatic forces between the hair fibers. This results in reduced frizz and improved hair combability.
Therefore, we can conclude that the pH of shampoos is one of the factors that most affect the aesthetics and hair health. Shampoos with pH value above 5.5 may irritate the scalp and aggravate frizz, but adding cationic agents in the product may help alleviate these aesthetic effects.
- Gavazzoni Dias MF, de Almeida AM, Cecato PM, Adriano AR, Pichler J. [The Shampoo pH can Affect the Hair: Myth or Reality?] Int J Trichology. 2014 Jul;6(3):95-9. doi: 10.4103/0974-7753.139078.
Paid content provided by in-cosmetics Latin America
About the author
Cleber Barros is co-founder and Technical Researcher at Vinia | Inovação Cosmética and a cosmetology consultant. He works in R&D as well as providing technical qualification in cosmetology.
Cleber Barros is the technical advisor for in-cosmetics Latin America.
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