You have probably heard about prebiotics, probiotics and postbiotics but without really knowing the difference.
Prebiotics are usually fibers extracted from fruits, vegetables, and honey. Bacteria use it as food and digest it with enzymes. Prebiotics are only food for good bacteria though, and are toxic to bad bacteria. The idea is to bring to our skin the good prebiotics in order to help our good bacteria already present to eat correctly and to develop.
Probiotics are bacteria, sometimes deactivated. They can be the same as good bacteria already present on our body, or not. Their main interest is to prevent bad bacteria from colonizing our different floras. What's interesting is that even bad bacteria are important for a healthy microbiome, it is only when they are dominant that skin concerns arise.
Postbiotics are molecules produced by good bacteria. These substances maintain a good environment for bacteria. Lactic acid, from Lactobacillus, helps maintain the acidic pH of the skin.