How common is it for side effects to occur while using nystatin cream? and are allergic reactions common at all?

The use of any medication can elicit an allergic reaction or a skin irritation. In general nystatin cream doesn’t for most people however everybody’s individual when it comes to these types of reactions and certainly possible

Itching and skin irritation, both mild and severe, have been reported while using nystatin cream, but those cases are rare. A delayed allergic reaction is possible as well, but this is also not common.