Provided are: a method of producing a therapeutic agent for skin lesions suitable for treatment or prevention of a skin lesion such as a bedsore; and a therapeutic agent for skin lesions produced by the production method. The method of producing a therapeutic agent for skin lesions characterized by including a mixing step of mixing earthworm castings with water and a collecting step of collecting vaporized water generated from a mixture obtained in the mixing step to obtain a liquid; and the therapeutic agent for skin lesions produced by the production method. It is preferred to further mix an organic substance together with the earthworm castings and the water in the mixing step.