The nature of the skin can be distinguished by factors such as skin water content, skin secretion status, skin pH and response to external stimuli. 1. Skin water content: If the water content of the stratum corneum is 10% to 20%, it mostly belongs to neutral skin. If the water content of the stratum corneum is lower than 10%, it may be dry skin. If the water content of the stratum corneum is around 20%, consider oily skin. 2. Skin secretion: neutral skin sebum secretion is usually moderate, does not show dry or greasy situation; dry skin hair sebum secretion is less, the skin is more dry, flaky; oily skin sebum secretion is exuberant, the surface of the skin is greasy and glossy, and easy to produce acne. 3. Skin pH: the pH of neutral skin is 4.5~6.5; the pH of dry skin is above 6.5; the pH of oily skin is below 4.5. 4. Reaction to external stimuli: neutral skin is more adaptable to external stimuli; dry skin is more sensitive to external stimuli; oily skin is generally not sensitive to external stimuli; and sensitive skin is highly reactive to external stimuli. There are many ways to distinguish the nature of the skin, it is recommended that patients go to a formal medical institution to consult a specialist to understand the relevant matters.