Although diarrhea is often defined as the frequent passage of slightly compacted stools, in the case of children it is more correct to say that it consists in one or more liquid stools in a day. This symptom is acute when showing many times in a single day, and tends to normalize in less than 2 weeks. Diarrhea is severe when accompanied by fever, vomiting, abdominal pain, a few times also by hematochezia, and eventually dehydration. In children younger than 2, diarrhea leads to dehydration in approximately 10% of cases, whereas life is seriously at risk in almost 1% of cases. There is also a special circumstance making this condition more severe: malnutrition. This is important in developing countries, where lots of people live either under the poverty line or in extreme indigence, and have no cultural background nor any element aimed to improve their hygienic conditions. All this goes hand in hand with such problems as result from the lack of drinking water, sewing system, or even housing or too many people living together, not to mention household garbage, the contact with domestic animals etc. It has been statistically calculated that, in these countries, children younger than 5 usually undergo 2 to 5 episodes of diarrhea in a year, which means to say that they suffer from this disease 20 to 30 days a year.