Local pigmentation in the human body is related to hormonal changes in the body and long-term friction. The inner thighs are often rubbed during exercise, especially some of the more obese friends are more likely to rub here, resulting in local pigmentation skin darkening. The exact cause is not known. But you can improve the pigmentation through laser treatment, such as Q755 laser, every three months for laser treatment, slowly fade. The same time also pay attention to weight control, obese friends need to lose weight to eliminate the causes of hyperpigmentation.