What are the things that invalidate Wudu?

Wudu is invalidated by anything exiting from the front or back private parts (such as urine, stool, or passing wind), the flow of blood or pus from the body in a way that spreads beyond the point of the wound, vomiting a mouthful, and falling into a deep sleep lying down or losing consciousness. Scholars differ on some secondary matters such as bleeding that doesn't spread or touching the opposite gender, so if a specific situation is unclear it's worth asking a local scholar which view your family generally follows.