The nature of corruption and why it occurs is a complex debate best left for scholars and theologians, however in the practical sense there are two forms of corruption. The most common and easily cleansed form is referred to as Transient Impurity. This Impurity is the result of contact with Unknown or death in any capacity and must be carefully monitored. However, it can be reasonably easily cleansed. If you are aware of Impurity within yourself and cannot cleanse for any reason, the common suggestion is to avoid physical contact or prolonged social contact with other people. If you must be around other people, gloves will mitigate the risk, as will physical distance.
The secondary form of corruption is referred to as Core Corruption. This corruption is far more dangerous and far more difficult to cleanse. Most mortals have no corruption at baseline though there are those who by virtue of their lineage may have some. This is seen most commonly among Tieflings or among those who may have had a particularly notable tragedy in their lineage. Corruption is, thankfully, more difficult to expose others to. Having a high level of Core Corruption can cause physical and temperamental changes to an individual until cleansed but cannot, typically, be unintentionally transferred to another through contact of any kind. Still, if you are aware of an unnatural increase to your state of Core Corruption, it is considered best to advise those around you and maintain caution to protect yourself and others while you work toward that cleansing.
The rituals for cleansing Impurity typically only take hours though can take days if the level of Impurity is particularly high or if the subject has a high level of Core Corruption as well. However, the rituals for cleansing Core Corruption begin at a matter of weeks of daily actions moving up to months-long rituals. If a subject has particularly strong Core Corruption, it is advised that the subject rest frequently in the process of purification so as not to overwhelm their system.