pH of Leave-on Hair Treatment and its Effect on Scalp and Hair

Regarding the pH of shampoo, conditioner, and hair treatments:

The recommended pH range for most hair care products, including shampoo, conditioner, and leave-on treatments, is generally between pH 4.5 and 6. This range is close to the natural slightly acidic pH of the scalp and hair (around 4.5-5.5).

Using products within this range helps to:

• Maintain the health of the scalp.
• Keep the hair cuticle flat and smooth, reducing frizz and increasing shine.
• Minimize damage and breakage.

You mentioned a leave-on hair treatment with a pH of 4.0. While the ideal range is typically 4.5-6, a pH of 4.0 is still acidic. Acidic pH levels generally help to flatten the hair cuticle, which is beneficial for smoothness and shine. Products with a pH below 3.5 can potentially cause hair damage over time, but a pH of 4.0 is not typically considered to be in this severely acidic range.

In comparison, alkaline products (pH above 7) are much more damaging to hair as they cause the cuticle to open, leading to dryness, frizz, and breakage.

Therefore, while pH 4.5-6 is often cited as the optimal range, a leave-on treatment with a pH of 4.0 is generally acceptable and unlikely to cause significant harm to the scalp or hair, especially compared to alkaline products. However, individual sensitivity can vary.