Phlegm (pronounce /flɛm/) is sticky fluid secreted by the mucus membranes of humans and other animals. Its definition is limited to the mucus produced by the respiratory system, excluding that from the nasal passages, and particularly that which is expelled by coughing (sputum). Its composition varies, depending on climate, genetics and state of the immune system, but basically is a water-based gel consisting of glycoproteins, immunoglobulins, lipids, etc.