Cosmetic composition for protecting skin from any stress generating free radicals or reactive species of oxygen, comprises a thiazolidine derivative as a main ingredient, in combination with an excipient. Cosmetic composition for protecting skin from any stress generating free radicals or reactive species of oxygen, comprises a thiazolidine derivative of formula (I) as a main ingredient, in combination with an excipient. X : O (preferred) or S. [Image] ACTIVITY : Tranquilizer; Dermatological. MECHANISM OF ACTION : None given.