The skin on the neck area of the feet appears black and cannot be cleaned by any amount of washing. Careful observation of the appearance of the black skin surface and the self-conscious symptoms is required to determine how the factors are formed. If this black skin is hard to the touch and is accompanied by significant itching, consider the possibility of chronic keratotic eczema. The condition is related to allergies, irritation, and prolonged scratching.
If the black area on the neck of the foot is simply a change in color, without any conscious symptoms, and the texture of the skin is consistent with normal skin, consider that it may be caused by long-term exposure to ultraviolet light or some radioactive substances, which is triggered by the increase in the number and volume of subcutaneous pigment cells. If the black area is secondary to eczema or dermatitis, it is possible that it is a simple pigmentation that will gradually recover on its own over time.