What pH level is considered best for shampoos used on previously lightened hair?

The pH level of 4.5 to 5.5 is considered ideal for shampoos used on previously lightened hair because this range closely mimics the natural pH of the scalp and hair. Lightened hair tends to be more porous and damaged, which makes it more susceptible to environmental factors, chemical processes, and moisture loss.

Using shampoos within this pH range helps to maintain the hair's acidity, which is essential for preserving the cuticle's integrity. A balanced pH can help minimize the risk of further damage and deterioration, as more acidic shampoos can help smooth the cuticle and reduce frizz, while also promoting moisture retention. Furthermore, this pH level enhances color longevity and vibrancy for hair that has been chemically treated or lightened.

In contrast, shampoos with a much lower or higher pH level could compromise the hair’s condition. Shampoos that are too acidic can strip the hair of essential oils, while those that are too alkaline may cause increased swelling and damage to the hair shaft. This makes the 4.5 to 5.5 pH range particularly beneficial for maintaining the health of lightened hair.