Probiotics are able to inhibit certain pathogens, their use to fight acne caused by the proliferation of Propionibacterium acnes, would be an alternative in topical bacteriotherapy. There are studies of in vitro antagonism¹. This study in vivo the antagonistic capacity of Lactobacillus acidophilus against Propionibacterium acnes in young people from 15 to 20 years old, with previous diagnosis of type II acne. First the evaluation of the in vitro antagonistic effect of Lactobacillus acidophilus against Propionibacterium acnes was performed. The measurement of the inhibition halos determined the concentration with antagonist effect 1×10⁸ cfu/ml, with this concentration four formulations were tested, of these four only one had an in vitro effect; this formulation was subjected to a test of irritability (Mexican standard Nom-039-SSA1-1993) IPC = 0.19 defines the formula as “well tolerated”, the study of cosmetic activity in vivo was performed with a non-invasive method of exploration , using the Visiopor PP 34N® bioengineering instrument as a result, a 48-hour decrease in average porphyrins of 78.3% was obtained in the total number of treated individuals, which implies a decrease in the population of P. acnes, the acne-causing agent.