Preventive actions are taken to prevent a potential problem, organizations try to address problems before they happen. Whereas corrective actions are taken after a problem has occurred.
According to the ISO 9000:2015 - Quality management systems - Fundamentals and vocabulary; it emphasizes the difference between corrective action and preventative actions. Corrective actions are taken after an incident occurs to fix and prevent the recurrence, whereas preventative actions are taken before the occurrence to prevent the potential problem. Preventive actions are proactive while corrective actions are reactive.
For instance; a pipe burst and a water flooding incident occurred. The corresponding corrective actions address the root cause of the flood, such as fixing old pipes. Contrary to this turning off the water source is a correction that eliminates the cause temporarily. But if the organization controls their pipes regularly and realizes that a pipe is going to burst, at that time they can take preventative actions to prevent the occurrence, before it happens.
Preventative action term is mentioned in several regulations and standards such as FDA, GMP, ISO standards (ISO 9001, ISO 13485). If we examine thoroughly the ISO Quality management standards, both are made a similar point.
According to ISO 9000, preventative action is an action to eliminate the cause(or causes) of the potential nonconformity and to prevent occurrence.
Likewise, according to ISO 13485, the following enlisted requirements should be documented in a procedure;
Determine the potential nonconformity (nonconformities)
Review the need for possible actions to prevent the occurrence
Plan and document the action(s) and implement it(them)
Verify that the action does not adversely affect the current requirements which are already complied with.
The last thing that the organization should perform at the end of each nonconformity management. Review the effectiveness of the taken action after a defined period.