Defense mechanisms are unconscious mental techniques used to reduce anxiety by keeping distressing thoughts out of conscious awareness. More mature defenses include altruism, humor, sublimation, and suppression. Common defenses are altruism, humor, suppression, sublimation, acting out, denial, displacement, dissociation, idealization, identification, projection, intellectualization, isolation of affect, rationalization, reaction formation, regression, splitting, somatization, undoing, and transference reactions. Transference and countertransference involve unconscious attitudes toward others based on past relationships that can help or hinder treatment.