As a type of lung infection, pneumonia is caused by bacteria, viruses, or even some fungi, or by inhaling certain chemicals. The infection causes inflammation in the lungs, and this causes the lungs to fill with fluid. A patient might have difficulty breathing, which is one of the most common symptoms of pneumonia. There are other symptoms too, such as fever, fatigue, yellow or green mucus, chills, shortness of breath, sweating, headache, loss of appetite, confusion, and coughing. Often the coughing will cause chest pain. Age is actually a factor in which symptoms a patient will get. Children 5 years of age or younger might experience fast breathing or wheezing, and infants may experience vomiting or difficulty with eating or drinking. Senior patients might not even have any immediately noticeable symptoms, but they might have a low body temperature, and if you pay close attention, you might notice they're experiencing some confusion. Usually, the symptoms of pneumonia are mild, but there are some factors that make pneumonia life-threatening. Patients who smoke or have lung disease, chronic lung problems, heart disease, or a weakened immune system may be at great risk. Chemotherapy patients, as well as infants, children, and patients 65 or over may also be at great risk. These patients require emergency medical care at a hospital because their case of pneumonia could be life-threatening.