Cupping very black is generally considered to be related to blood stasis, heat toxicity, cold condensation, etc. It is recommended to go to a regular hospital for cupping.
Due to the different evil qi in the body, different skin changes will appear at the location of cupping, also known as canning spots, canning marks and so on. If the skin is purple-black after cupping, accompanied by localized fever, it is mostly related to the blazing of heat-toxin (too much fire in the body); however, if you see black ecchymosis on the skin at the place of cupping without fever, it is considered to be related to the stasis of blood and cold condensation, which leads to the poor operation of qi and blood.
If the color of the skin gradually deepens after each cupping treatment, it generally suggests that the condition is aggravated; if the color of the skin gradually becomes lighter, it suggests that the condition is gradually improving. If the skin is broken or allergic, cupping is not allowed to avoid infection.
Cupping is recommended to be operated by a professional Chinese medicine practitioner, do not do it by yourself to avoid damage to the body caused by wrong operation.