How to Avoid Event Recursion
When working with event receivers, there is always a chance that your code will trigger the same event multiple time. As a result, the application pool will be recycled, which will be a poor performance by SharePoint Site.
To avoid this issue use EventFiringEnabled property which is exposed by the SPEventProperties base class and is available within event receivers.
You should set false and true before updating an item and after updating that item respectively.
Below is the code to avoid Event Recursion
public override void ItemUpdating(SPItemEventProperties properties)
EventFiringEnabled = false;
EventFiringEnabled = true;