Does the pH of your shampoo affect your hair?

The pH indicates the acidity, alkalinity, or neutrality of a given medium. The pH scales range from 1 to 14. Solutions and substances with a pH below 7 are considered as acidic and above 7 alkaline.

Your hair is a protein that carries a charge. Your hair can be positive, negative, or neutrally charged. The hair is neutrally charged when the pH is around 3.76. It will be slightly lower for bleached or damaged hair. The scalp has a pH somewhere between 4.5 and 5.5.

So most shampoos are pH balanced and have a pH between 4 and 7. This will not lead to any issues for the scalp (also if a shampoo is slightly higher or lower you don’t need to panic).

This means that the hair becomes more negatively charged and the problem with these negative charges is that they repel each other, leading to friction, and thus there will be difficulty combing and frizzy hair.

This is also why some shampoos are promoted as acidic because the low pH of the shampoo minimizes the negative charge and gives you less frizzy hair.

And this is also the reason why sometimes apple cider vinegar (ACV) is used to rinse the hair. ACV has a pH ranging from 3.1 to 5. So when ACV has a pH near 3.67, the increase in negative charge is minimized, leading to less frizzy hair. But, if ACV is not diluted in water, ACV may be too caustic for direct application to the hair and may lead to damage. It can also be irritating to the eyes and acutely inflamed skin (so it’s better to not use ACV).

Besides, there is just a very simple solution to that negative charge and that is using a cheap and simple conditioner.

Conditioners contain a cationic ingredient that carries a positive charge and thus binds to the negative charge of the hair and neutralizes it resulting in smooth and combable hair.  

Note: pH lower than 2 or higher than 9 can be damaging for the hair, but reputable liquid shampoos don’t have that pH.