The causes of skin pigmentation may be related to friction, post-inflammatory hyperpigmentation, endocrine disorders and other reasons. 1. Friction: Because some parts of the body will be repeatedly rubbed to cause the skin protective reaction, that is, by thickening, hardening to fight against friction in order to reduce the damage to the skin, thickening of the skin will have melanocyte function enhancement, so there will be the phenomenon of skin pigmentation. 2. Post-inflammatory hyperpigmentation: when the body’s skin suffers from eczema, dermatitis and other inflammatory diseases will appear after the recovery of the phenomenon of skin pigmentation. 3. Endocrine disorders: endocrine imbalance is also a key cause of skin pigmentation, physiological period and pregnancy of the body’s estrogen level changes, can affect the production of skin pigmentation. When patients have skin pigmentation, it is important to first clarify the cause of the disease, and then according to the specific cause of the disease to carry out targeted treatment.