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Science Class 05: pH

pH is something a lot of us learned about as kids in science class (the original one, not the K18 one).  We learned things like lemonade or orange juice are acidic and tap water is alkaline. But you don’t usually come to us for beverage knowledge—so where does the hair come in?

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One of the key conversations to understanding hair health is centered around those two little letters we’ve heard so much about: pH. Let’s dive in. 

What is pH?

A quick refresher to center you before we dive deeper: pH is a unit of measurement like meters, feet, or pounds. —specifically, it measures the amount of hydrogen (H+) ions in a solution or the “potential of Hydrogen.” We talk about the pH of substances by their acidity or alkalinity; more Hresults in LOW pH (acidic), while fewer Hresults in a HIGH pH (alkaline or basic). The range goes from 0-14 with 7 being the neutral mark. All things with a range above 7 are considered alkaline, all below are considered basic. 

There are two important features of pH to understand: first, it is the measure of Hions in solution, which means it requires the presence of water to be measured in the first place. This means that anhydrous (or water-free) products like oils do not have a pH. 

FUN FACT: oil cleansers that claim to be pH-balancing can’t be! The more ya know. 

Second, the measurement of Hions is done on a logarithmic scale, which means that for every unit change of 1 on the scale (for example, from 5 to 6) translates to a TENFOLD increase or decrease. Move 2 units and the amount of Hchanges by 100, 3 units and Hchanges by 1,000, and so on. That’s the long way of saying minor changes in pH can alter a chemical environment dramatically! The pH of human blood must be kept within such a precise range that any shift outside of 7.35 – 7.45 becomes a serious medical condition.


How does it relate to my hair?

Your hair has its very own pH range which can play a significant role in hair’s overall health. Healthy hair has an optimal pH range of 4.5–5.5 and is a self-regulating environment, meaning without any outside factors introduced, your body has everything it needs to keep this ranges in check and prevent the growth of things like fungi and bacteria. Introducing something foreign or something not optimized with the same pH level as your natural range can throw the pH all out of whack. When the range is imbalanced (as can happen with many different factors that we’ll get into) hair becomes vulnerable.


Science Class 05: pH

Optimal pH for Hair

When the hair shaft is within range, its structure is most resistant to damage. At optimum pH, the acidic groups of amino acids are negatively (–) charged, the basic groups are positively (+) charged. These opposite charges attract each other, creating ionic bonds or “salt linkages” that contribute to the fiber’s strength. Hair proteins are in their best condition and exhibit the best thermal stability when kept within this range. 

When the pH environment of the hair drops below or exceeds this range, its structural integrity is compromised and damage may occur. 


Styling + pH

Humans put A LOT on their hair. Every product has its own pH that’s being introduced to these environments and potentially disrupting that balance. Your optimal hair range is about a 4.5-5.5, but the average dry shampoo sits around an 8. Yikes. 

There are product options that prioritize "pH-balanced" formulas which are designed to maintain the healthy pH of your hair. i.e. they won’t introduce a new pH level or knock the healthy environment off balance.  However, many products either don’t disclose product pH levels or don’t prioritize creating within the same range at which hair is optimal. High pH products can cause hair to expand. Low pH products can cause hair to contract. Both extremes can lead to damages that result in dry and frizzy hair.

In a 2014 research article titled The Shampoo pH Can Affect the Hair: Myth or Reality? researchers measured the pH of 96 consumer shampoos—more than 65% of these had a pH greater than 5.5, and some were even measured as high as 9! They concluded that high pH (alkaline) levels might increase the net negative electrical charge on hair's surface. Those negative electrical charges, coupled with a more highly swelled cuticle, increase friction between the fibers. This increased friction could lead to cuticle damage and fiber breakage. 

Conversely, lower pH shampoos were shown to cause less frizzing. The researchers suggest balancing the pH in your hair naturally by using hair care products with a lower pH, closer to your hair's natural pH level.

Chemical services + pH 

Most treatments use chemicals to swell or open up the outer layer or the cuticle of your hair or change the chemical bonds that hold your hair together—they do this, by shifting the pH levels. Bleaching solutions average between a pH range of 9-11, perms can be 9-10.2, and relaxers average 8.5-13. The worst are hydroxide relaxers, which cause extensive damage to the hair’s proteins.  

At very high pH, the normally positively-charged amino groups lose an H+ resulting in an uncharged group, again breaking the salt link bonds. In addition, the fiber swells significantly more at alkaline pH, becoming more porous. The scales of the cuticle spread out significantly more as pH increases. 

Water + pH

When it comes to throwing your pH balance off, exposing hair to product or damaging chemical services make sense, but did you know water can just as easily be a culprit?  

Water naturally has a pH of 7. It's the middle of the pH scale and is considered neutral. However, that pH number is for distilled water (and we don’t know about you, but most of us don’t use distilled water to wash our hair)

Depending on where you live, just washing your hair with water can change its pH. With an average pH range of 6.5-9.5 a quick rinse alone sets the environments off-balance.  


the sparknotes

The ultimate goal is to keep hair’s pH balanced to maintain hair’s resistance to damage.

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