Understanding pH Balance and Hair

I’m revisiting this topic again and am not sure if it’ll turn into a two or three part blog, but it’s an important one so bear with me as I discuss the science-y part first. If you’re ready to get your nerd on here we go...

Measuring pH has great utility for understanding the behavior of hair products on the strands and also assists in predicting the hair’s response to these products. Real quick, the term pH is short for potenz hydrogen, translated directly from Danish as “hydrogen strength”. The pH of a substance specifically indicates the amount of positive hydrogen cations (shown as H+) and negative hydroxide anions (shown as OH-) a solution contains.

When the concentration of hydrogen ions is higher, a substance is considered acidic; if the concentration of hydroxide ions is higher, then the substance is alkaline (because they’re not water based and have neither H+ nor OH- components, products such as oils and alcohols do not have a pH).

The pH scale ranges from 0 to 14. At the middle of the scale lies the neutral pH of 7. “Pure water” is an example of a neutral pH.

The pH scale ranges from 0 to 14. At the middle of the scale lies the neutral pH of 7. “Pure water” is an example of a neutral pH.


When a substance has a low pH reading of 0 to 6.9, it’s considered acidic. Hair and skin are covered by a thin, slightly acidic film called the acid mantle. Healthy hair and skin both have acid mantles with pHs in the 4/5.5 range. This acid mantle is more important for the skin where it acts as a barrier to viruses, bacteria and other contaminants that may try to enter the body and these contaminants, which are primarily alkaline, are neutralized by the body’s protective acid mantle.

Maintaining the acid mantle is also very important for our hair. Hair responds to pH very distinctly. Low pH substances affects the hair shaft by constricting the cuticle layers, causing them to lie flat and tightly against one another. In this state, the inner cortex of the hair strand is thoroughly protected. Tight and contracted cuticles also allow the individual hair strands to move freely past one another, and the uniform surface also better reflects light, which creates that shine and sheen. Neutralizing shampoos, conditioners, and natural substances such as lemon and apple cider vinegar fall into the acidic category.

Alkaline or Base

A pH of 7.1 to 14 is considered basic or alkaline. High pH substances cause the hair’s cuticle scales to "open" and the hair shaft to swell and lift. Although water is neutral, it’s roughly 100 times more alkaline than our hair. Hair is acidic, but when water (which bears a higher pH of 7) interacts with our hair, the cuticles lift slightly in reaction to the waters more alkaline pH. Relaxers, permanent hair colors also fall into the alkaline category.

Lifted cuticles are what’s responsible for tangly, dry looking hair that doesn’t shine, have sheen or hold moisture well. When the cuticles are lifted, the cortex is exposed and the hair becomes weaker and more vulnerable. It’s very important that the pH of our hair return to its normal 4/5.5 range after using an alkaline product. Damage to the hair strand is often imminent if the cuticles are not returned to their normal “closed” or tight position.

Regulating product pH is important in healthy care regimen. Great care must be taken to ensure that hair products used throughout your regimen contribute to restoring and maintaining your hair’s natural acid balance. Because the hair must maintain its acidic pH mantle to remain healthy, products that keep the hair within 4/5.5 are ideal. When the hair’s pH becomes too high or too low on the scale, the hair is always changed or damaged. Extremely high or low pH drastically affects the protein structure inside the hair’s cortex. 

I mentioned this before, but keep in mind that pH ranges are logarithmic (see graphic above), which means that each increase in pH level represents a tenfold increase in the number of hydrogen ions. Thus, a jump in pH from 5 to 6 is not an increase in strength of 1 but rather, an increase of ten times the strength. By the same token, a pH of 8 is 100 times more alkaline than a pH of 6. So avoid subjecting your strands to pH extremes for extended periods of time.

More in part 2 tomorrow.

Source: Hair Structure and Chemistry Simplified. Sciencey-blog by Wendy.

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