PH value represents the degree of acidity and alkalinity of skin,ranging from 0-14.Generally,0-7 belongs to acidity,7-14 represents alkalinity.Degree around 7 is neutral.
Ordinarily, PH value of healthy skin is 5.0-5.6,belonging to faintly acid.As a result,we should choose faintly acid prodcuts for skin care and it is suitable for our skin.
However,some facial cleansers are often mildly alkalinity.They have very strong function on cleaning oil ,so
pepole who are oily skin tend to use this kind of facial cleanser.But dry skin feels uncomfortable and dry.Because alkalinity stimulates skin a little and oil on skin is cleared too much.
In my opinion,it is better to use weak acid skin care products,such as washing face,which is depending on your skin.You'd better not use skin care products whose PH value is more than 8.However,low PH also not an option,so the best option is between 5.5-7. Oily skin can choose products whose PH value is slightly higher.The PH value of tears is around 5.5.So healthy skin usually choose products around 5.5.