There are many causes of sputum, the most common being upper respiratory tract infections, bronchitis, chronic bronchitis, lung abscess, pneumonia, tuberculosis, bronchiectasis, lung cancer and other respiratory diseases.
In addition, pleural diseases such as abscess chest and pleurisy, cardiovascular diseases such as left heart failure, environmental exposure to dust, metal powders, allergens, irritating and corrosive gases, and long-term smoking are also causes of sputum.