We’ve all seen references to pH on shampoo bottles and many other products. But how many of us know exactly what pH actually means?

pH refers to the acidity or alkalinity of a solution, and it’s measured on a scale of 0 to 14; 0 indicates extreme acidity, 7 is neutral (pure water has a pH of 7) and 14 indicates extreme alkalinity.

When the body is functioning normally, urine is slightly acidic and blood is slightly alkaline, but body imbalances can change these pHs. Hydrochloric acid, produced in the stomach to break down food, has a pH of about 1.5, so it is highly acidic. 

Because hair and skin are solid, they do not have a pH. However, liquids that coat the hair and skin do have a pH – so the products we use can influence the hair’s structure and affect the balance of microorganisms on the skin’s surface through their alkalinity or acidity. Any extreme on the pH scale is damaging to hair and skin.

The sweat and sebum (oil), produced on the skin’s surface create what is known as the ‘acid mantle’. Sweat has a pH close to 7 and sebum has a pH close to 5, so the acid mantle has a pH of about 5.5. At this slightly acidic pH, microorganisms on the skin’s surface are kept under control. Children produce no sebum so their acid mantle is closer to 7, which explains why children are more prone than adults to ringworm (caused by different fungi) on the scalp.

When sebum is allowed to accumulate on the scalp it decreases the scalp’s pH and allows yeast to thrive. Excess yeast is associated with dandruff and seborrheic dermatitis, so medicated shampoos are formulated to raise pH, kill the yeast and, consequently, reduce any scaling. Maintaining the skin’s acid mantle at the right pH of around 5.5 is important for its health and integrity.

That is why, for a healthy scalp, the shampoos you use should also have a pH of 5.5. Unfortunately, many shampoos do not list their pH on the label so you have to contact the manufacturer to find out the pH.

There is another reason why we should use shampoos and conditioners with a pH of 5.5, which has to do with the chemical bonds in our hair. Hair strength and elasticity are maintained in part by the electrostatic attraction of positive and negative ions in the hair’s keratin chains, known as ionic or salt bonds. These bonds are strongest when solutions applied to the hair have a pH of 5.5. A higher or lower pH will reduce the number of salt bonds and, therefore, weaken the hair. It will also create an imbalance of positive and negative charges, causing the cuticle of the hair (the outside protective layer) to open up, which reduces the hair’s sheen and makes it more prone to damage. Most conditioning rinses for the hair have a pH of about 5.5 to help close up the cuticle and maintain the ionic bonds.

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