Coughing up yellow mucus can indicate that your body is fighting off some sort of infection. Yellow phlegm is often developed in the early stages of an infection, and it turns green the longer the infection lingers. Here are some possible health conditions related to coughing up yellow or green phlegm:

• Viral bronchitis
• Viral pneumonia
• Sinusitis
• Cystic fibrosis

If you have bronchitis, your cough may bring up thick yellow-grey mucus (phlegm), although this does not always happen. However, the presence of green or yellow mucus does not always indicate a chest infection, and there are several other causes. If you are coughing up yellow mucus, it is always best to check with a healthcare provider to determine the underlying cause and receive appropriate treatment.