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Dermatothlasia is a cutaneous neurosis characterized by a person's uncontrollable desire to rub or pinch him/herself to form bruised areas on the skin, sometimes as a defense against pain elsewhere.
References
James, William D.; Berger, Timothy G.; et al. (2006). Andrews' Diseases of the Skin: clinical Dermatology. Saunders Elsevier. ISBN978-0-7216-2921-6.