Your hair strands and scalp have different pH levels, so shampoo (that touches the scalp) and conditioner (that is mostly on the strands) have different pH levels too. The hair cuticle layer is acidic, with a pH of around 3.67 to 4.5. This acidity helps to keep the hair structure closed and protects the hair from damage. It also helps to keep the hair's natural oils and moisture locked inside. The scalp, on the other hand, has a pH of around 4.5 to 5.5. This is slightly more alkaline than the hair, but it is still on the acidic side. The scalp's acidity helps to protect it from harmful bacteria and other microorganisms. Shampoos and conditioners are designed to match the natural pH of hair and scalp. Using products with the right pH for your hair and scalp is important. If you use products with a pH that is too high or too low, it can damage your hair and make it dry, frizzy, or brittle.