There are many reasons of haemoptysis !! It may be due to weak capillaries of the lungs causing it to bleed even on coughing. It might also be a old injury inside the bronchi caused by bronchoscopy, which bleeds spontaneously or due to cough.
The other reason for haemoptysis are bronchitis and pneumonia
most commonly, but also core pulmonale , lung neoplasm (in smokers, hemoptysis is often persistent), aspergilloma, tuberculosis, bronchiectasis, coccidioidomycosis
, pulmonary embolism
, pneumonic plague
, and Cystic Fibrosis.
hope my info helped you
Dr Hari Om Chandrakar