Frizzy hair? Your shampoo pH might be the culprit.
Many of you heard of “pH balanced” shampoos or even bought some of those, and maybe you wondered what does it mean.
I personally found these labels very confusing for the consumers. As a chemist, the first time I saw the “pH balanced” label I thought that maybe the pH is 7 (what we call neutral or balanced in chemistry). As a second thought I was asking myself: “Balanced to what?” You need to have a reference point.
The reality is there is no standardized value for the pH of a shampoo and pH value varies among different shampoos on the market. A research group in Brazil (2) analyzed 123 shampoos on the market and found pH values anywhere from 3.5 to 9.
To understand better how pH influences the hair, lets first define pH:
What is pH?
Described for the first time by the Danish biochemist Søren Peter Lauritz Sørensen in 1909, pH stands for “power of Hydrogen”(1). The pH scale measures how acidic or basic a substance is. It ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic, and a pH greater than 7 is basic (or alkaline). An increased concentration of (negative) hydroxyl ions [OH-] will make a solution more alkaline, where one with increasing concentration of (positive) hydrogen ions [H+] will make it more acidic.
How does the shampoo pH influence my scalp and hair strands?
Shampoos are not cleaning only the scalp they have a strong influence on the hair shaft as well. The pH of the scalp is 5.5 and the hair shaft pH is 3.7 (2).
Any product applied on hair that has pH higher than 3.7 causes an increase of the negative charge on the hair strand which is actually an increase of static electricity and provokes repulsion between hair fibers, causing the “frizziness” effect. Water is more alkaline in nature so when the hair is rinsed, it becomes negatively charged and repels the anionic cleansing agents (surfactants), washing away the residues (2). Furthermore, hair has an increased capacity to absorb water in alkaline environment: water penetrates the cuticles which open up and breaks the hydrogen bond of the keratin molecules, causing increased cuticle removal and breakage (3).
Therefore shampoos with pH higher than 5.5 will induce frizz on normal and dry hair, and will be hard to detangle.
In order to overcome this, the pH of the shampoos is reduced to the “balanced” range (3.5 – 5.5) by addition of mild acidic substances, such as glycolic acid or citric acid. Also the hair shaft negative charges can be reduced by introduction of cationic surfactants.
This is the reason that cationic surfactants are the main components in conditioners and leave-in crèmes.
On the contrary, higher pH in a shampoo can induce the “volumizing” effect to an oily hair.
Many clarifying shampoos (used to remove a lot of buildup on the hair) use alkaline ingredients to swell the hair shaft and allow the surfactants to penetrate more deeply. Persons who use these shampoos need to use also an acidic conditioner to protect the hair shaft by contracting it and keeping the moisture inside (4).
Shampoos for colored, chemically treated hair should be formulated with a lower pH (around 4-4.5) to compensate for the raised cuticles and hair damage. And also persons with curly hair that is usually drier than the straight hair should use shampoos with lower pH.
Because the scalp pH is 5.5 like the rest of the skin, shampoos that target scalp treatments should not have pH higher than 5.5.
Pediatric shampoos have a pH around 7.0 because of the “no-tear” concept and they are not intended to treat scalp.
My hair looked and felt better when I lived in Florida
When travel or move to another location, you might have observed that your hair feels and look different, even when you use the same shampoo. That is because the water in different areas has different hardness. Hard water (which has a higher dissolved mineral content) is more alkaline (higher pH) than softer water and so the difference in hair behavior. Well water from areas that have a lot of limestone is often hard. Water that comes from lakes and rainwater is often devoid of minerals, making it soft. Adding some lemon juice and vinegar in your rinse water (to decrease the pH) are often helpful to deal with hard water issues.
- Acidic ingredients will harden and contract the hair, while alkali ingredients expand and soften the hair shaft, making it more prone to frizz and breakage.
- Enough of moisture and oil in the hair are signs of good healthy growth, which can get affected when the acidity is disturbed (5).
- In general, it is better to use shampoos with pH lower than 5.5 and avoid the use of clarifying shampoos as much as possible.
- There is no such thing as “the best shampoo” on the market. Each person should look for the “suitable shampoo” for her/him, as we all have different hair types, textures, concerns, daily activities, and live in different environments.
- Gavazzoni Dias MFR, de Almeida AM, Cecato PMR, Adriano AR, Pichler J. The Shampoo pH can Affect the Hair: Myth or Reality? International Journal of Trichology. 2014;6(3):95-99.
- Robbins CR. The physical properties and cosmetic behavior of hair. In: Robbins CR, editor. Chemical and Physical Behavior of Human Hair. 5th ed. New York: Springer-Verlag; 2012
- Bouillon C, Wilkinson J. The science of Hair Care, Ed. Taylor & Francis, London, 2005, 92-139.