If the inner thighs become black, clinically it may be caused by a variety of reasons, such as friction caused by chronic inflammatory stimulation, or with the body’s hormone level secretion, disease, as follows: 1, friction caused by chronic inflammatory stimulation: many people in the area because of frequent friction caused by chronic inflammatory stimulation reaction, will form a local melanin deposition phenomenon, and such melanin deposition is also due to mechanical stimulation 2, with the body hormone level secretion: this situation may also be related to the body’s hormone level secretion, especially some people due to the correspondingly high level of estrogen in the body, may also stimulate the activation of local melanocytes, resulting in the phenomenon of blackening. 3, disease: some people may be and local inflammatory stimulus response Related, such as the emergence of eczema or ringworm, etc.