It is important to understand that while the human body does indeed contain microorganisms, such as bacteria, that play important roles in maintaining overall health and homeostasis, not all bacteria are harmless. Some bacteria can cause illness, and can even be life-threatening, especially to people with weakened immune systems. Proper hand hygiene, including washing your hands thoroughly with soap and water, is one of the most effective ways to prevent the spread of harmful bacteria and infection. Even if you are the only person involved and you already have some of the bacteria in your body, washing your hands after using the toilet can still be beneficial, as it can help to remove fecal matter and other harmful bacteria that could cause infection or make you sick.