When it comes to bacteria, many people have a pretty simple view: Germs are bad, and our lives should be as free of them as possible.
But an alternate idea suggests just the opposite: Germs are a necessary part of a healthy immune system, helping our body's defenses beef up and fight future illnesses. When a person's exposure to germs is decreased, problems may arise.
The idea is called the hygiene hypothesis. For years, scientists have suspected that it played a role in how diseases affect people in the modern hand-sanitized world, but they never had any specific evidence.
But a new study from researchers at Brigham and Women's Hospital in Boston has changed that.