Darkening of the intimate sides and inner thighs may be caused by physiological factors such as friction, or it may be caused by post-inflammatory hyperpigmentation, acanthosis nigricans and other diseases, which can be improved through general treatment, medication, physical therapy and other ways. 1. Physiological factors: long-term friction stimulation may cause darkening of the intimate sides and inner thighs, it is recommended to minimize friction in daily life and wear loose, soft clothes to avoid aggravation of symptoms. 2. Post-inflammatory hyperpigmentation: Eczema, ringworm and other inflammatory skin diseases can cause local post-inflammatory hyperpigmentation, which can lead to intimate sides and inner thighs black. Usually can subside on its own, if necessary, can follow the doctor’s instructions for external use of retinoic acid ointment, azelaic acid and other drugs, can reduce the local coloration. You can also choose laser treatment, the use of laser photothermal effect, lightening hyperpigmentation. 3. Acanthosis nigricans: darkening of the inner thighs on both sides of the intimate may also be caused by acanthosis nigricans. You can follow the doctor’s instructions to use hydroquinone cream and other drugs, can reduce hyperpigmentation. You can also choose laser treatment, the use of laser broken melanin cells, to achieve the effect of lightening the pigmentation. There are more reasons for the darkening of the inner thighs on both sides of the private, after excluding physiological factors, it is recommended to go to a regular hospital for examination, to clarify the cause of the disease, and to cooperate with the doctor to carry out standardized treatment.