Though dairy products are considered one of the four basic food groups and an important part of the diet, in one specific situation milk can be responsible for causing a type of rampant decay. This decay process happens when a child goes to sleep while breast-feeding and bottle-feeding. The milk is collected on the roof of the mouth and tongue, and the upper front teeth are bathed in it. During sleep, the flow of saliva is reduced and the natural self-cleansing action of the mouth is diminished. The sugar content of the stagnant collected milk is changed to acids which cause decalcification (softening) of the enamel, resulting in extensive decay called “nursing caries”.