Background and objective: Staphylococcus epidermidis is an autologous bacterium that is beneficial to skin health. Our goal was to develop a novel, personalized basic cosmetic that exploits this characteristic. Methods: We conducted a double-blinded, randomized clinical trial on augmentation with S. epidermidis as a pilot study, in which S. epidermidis was collected from the subject, cultured for proliferation, and then continuously applied to the subject's own face before sleep twice per week for four weeks in order to increase colonization levels. Results: The results showed that this treatment increased the lipid content of the skin and suppressed water evaporation, thereby markedly improving skin moisture retention. Moreover, augmentation with S. epidermidis maintained a low acidic condition on the skin surface. The low risk of undesirable effects induced by augmentation with S. epidermidis was also confirmed by measuring erythema and melanin levels. Conclusions: These results may serve as a driving force to accelerate the development of novel, personalized basic cosmetics. (C) 2015 Japanese Society for Investigative Dermatology. Published by Elsevier Ireland Ltd. All rights reserved.