Demodex was first identified over 150 years ago, but only recently has it attracted wider interest as a contributor to chronic diseases such as acne rosacea or marginal blepharitis. Demodex is commonly found in the human population, in skin sebaceous glands or follicles. The frequency of Demodex infection increases with age, as it is mainly diagnosed after the age of seventy; however, it can sometimes be found in children and teenagers. Demodex is supposed to contribute to the development of marginal blepharitis or acne rosacea, but the pathogenic mechanisms have not yet been explained in detail. These diseases are chronic and the long-term treatment effects are not satisfactory. This paper presents the characteristics of Demodex as well as its prevalence in the pathogenesis of eye and skin diseases, and describes the diagnostics and treatment of these disorders (Adv Clin Exp Med 2014, 23, 2, 295-298).