Probiotics are live microorganisms which when ingested in the right amount helps with maintenance of the gut microflora. Prebiotics on the other hand are nothing but fibres that act as food for the probiotics and helps them grow. The only caution that needs to be observed while giving probiotics is to be clear about the strain that is being given and the amount else the probiotic may not be effective. On the other hand prebiotics being natural fibers have no such side effect associated with them.