The hair itself does not have a pH value. What we call pH value refers to the pH value of the secretions around the hair. pH value is the indication of acidity and alkalinity, which refers to how much acidity and alkalinity there are in the aqueous solution. It is expressed as numbers at 25℃. From 0 to 14, 7 is neutral, above 7 is alkaline, below 7 is acidic, and the pH of the hair between 4.5 and 5.5 is the best health state. Because when the hair encounters alkalinity, the cuticle layers will open and split, the hair becomes rough and porous, and the effect of perming and dyeing cannot be achieved. The cuticle layer is closed when encountering acid, and the hair maintains a natural pH value of 4.5 to 5.5. The hair has good texture and luster, and it is easy to achieve the effect of perming and dyeing.