The human skin presents a diversified microbiota, which influences the body homeostasis and its protection. The unbalance of this microbiota leads to skin diseases, like atopic dermatitis (AD). AD is characterized mostly by increased number of bacteria Staphylococcus aureus, decrease in microbial diversity and intense inflammatory response. The most common bacteria skin species found in a small number in AD are Staphylococcus epidermidis and Staphylococcus capitis. They produce molecules that have the power to inhibit growing of S. aureus by quorum sensing mechanisms. The quorum sensing is a bacterial intercellular communication system, in which specie or gender have specific molecules, that can be a peptide or a polysaccharide, to communicate and respond at the same way to an external stimulus. Thus, this project aims to study which substances are released by S. epidermidis (ATCC 12228) and S. capitis (subsp. capitis ATCC 27840) through quorum sensing and its impacts on S. aureus (ATCC 6538) colonies and in the skin microbiota, assessing a possible treatment for atopic dermatitis using pre and post biotics. Liquid chromatography (HPLC - DAD - AGILENT, Infinity 1260) and mass spectrometry (Bruker Daltonics - autoflex™ speed MALDI-TOF/TOF) were used to identify PSMs among the S. epidermidis and S. capitis proteins differentially regulated by quorum sensing during growth in BHI (Brain and Heart Infusion) All strains were propagated at 37 °C. Microbial growth was monitored by absorbance at 650 nm (BioPhotometer plus – Eppendorf model 6132), comparing with the growth pattern of the cultures whether it occurred at the stage of decline or cell death of the bacteria. After this period, the broth was centrifuged (HERMLE Z 366 K) at 4500 rpm for 5 min at 4 ºC. The supernatant was recovered and vacuum filtered (45 µm). A liquid-liquid partition was carried out in a separating funnel, with 1/3 of the volume of ethyl acetate water (Scientific Exodus) being added to the filtered solution. Three extractions per volume were performed. After extraction with ethyl acetate, extraction with n-butanol was performed in the same separation flask three times to remove molecules with different polarities from the microbial supernatant. In the next step the extract was evaporated in a rotary evaporator (BUCHI R-210), the samples were reconstituted in methanol solution (brand, 100% P.A) and filtered (0.2 μm Nylon filter) and analyzed in the HPLC-DAD equipment. In parallel, an extract of the culture medium (BHI broth) was made under the same conditions already described, which was used as a negative control. It was possible to obtain an absorption spectrum in UV light by HPLC-DAD equipment of extracts of S. epidermidis, S. aureus and S. capitis with ethyl acetate and n-butanol at two wavelengths (254 nm and 360 nm). The pellet obtained by centrifuging the broth was washed with 10 ml of PBS solution and centrifuged again. The supernatant was discarded, washing and centrifugation process was repeated. The remaining pellet was treated with 1 ml of cell lysis buffer diluted in PBS. The samples were sonicated in 3 cycles of 20 s with amplitude equal to 40 and then centrifuged. The samples obtained from the pellets were analyzed by Mass Spectroscopy. Recent papers have already showed the importance of the agr systems for Staphylococcus sp, although we could not find a paper that expands this knowledge to an effective treatment. In this context we were able to identify the systems using the HPLC and Massas spectroscopy, and evaluated the use of this systems in vitro, to control the biofilm formation of S. aureus. The next step is challenging the bacteria with pre and post biotics, in a cosmetic formulation, evaluating the PSMs expression, increasing the S. epidermidis and S. capitis ones to inhibits S. aureus agr activity.