A prolonged bout of diarrhea or vomiting can cause the body to lose more fluid than it can take in. The result is dehydration, which occurs when your body doesn't have the fluid it needs to function properly. Severe dehydration can cause your kidneys to shut down. Though some types of diarrhea, such as those due to other medical conditions, are unavoidable, infectious diarrhea can be prevented. The most important way to avoid diarrhea is to avoid coming into contact with infectious agents that can cause it. This means that good hand washing and hygiene are very important.