Mouth breathing means that the child inhales and exhales most of the air through the mouth. One can put the face close to the children’s nose and mouth and ask them to exhale to feel the warmth of their breath to detect mouth breath. Placing a mirror in front of the nostrils will reveal which side of the nose has an obstruction. Factors such as polyps, severe nasal septum deviation, respiratory system problems or adenoid inhibit such people from breathing naturally through their nose. These people sleep and breathe with their mouths open, a condition also known as "adenoid," where they are often said to have a long face and a long high-arched palate. They also often suffer from crowding due to lack of space, orthodontic problems, and backward mandibular rotation. Mouth breathing causes the mouth to dry and can increase the decay rate as well as gingivitis.