What is the pH of healthy natural hair? Why does it matter?

pH measures how acidic or alkaline a substance (usually a liquid) is. Healthy hair and skin both have a pH ranging from 4.0 to 5.5 (this is acidic).

This film of acid that covers skin is called the acid mantle; it acts as a barrier to undesirable toxins, viruses and bacteria that try to enter the body. As most of these contaminants are alkaline they are neutralised by the body's acid mantle. Put simply, the scalp's acidity protects it from infection.

What is the pH of shampoos?
Shampoos are normally mildly acidic with a pH of 4 to 6.

What is the pH of conditioners?
Conditioners are normally more acidic than shampoos with a pH of 3.5 to 5.0.

Is the decrease in pH as we move from shampoo to conditioner intentional?
Yes. The lower pH of the final product used in the cleaning process helps to seal off the hair; sealing the hair means fibres are smoothed down and moisture is held in better.

What does this mean for your hair regimen?
It is much better to use products in the same product line as they are designed with this fall in pH from initial to final product in mind. 

For example, the shampoo of one brand may have a pH of 4.5 and the conditioner 3.5 meaning that your hair is properly sealed off. But if you then go and use a conditioner of another brand whose pH is 5.0, this sealing off process won't happen properly.

If you want to mix brands get pH paper to make sure that the pH falls as you move from the first product in the cleaning process to the final one.

What is the pH of relaxer and permanent hair colouring agents?
They are all alkaline with a pH ranging from 10 to 13.

What is the consequence of using these strongly alkaline products in hair?

Cross-section of hair

• The hair cuticle is lifted resulting in drier hair and a loss in shine
  
• The lifted cuticle exposes the cortex of hair making it weaker and more vulnerable to breakage.

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What happens to hair at different pH levels?

Reference: The Science of Black Hair, pages 44-45

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