What causes bronchiectasis? 

Bronchiectasis is caused by a cycle of inflammation and infection that damages the walls of the bronchial tubes, leading to permanent widening and scarring that prevents the lungs from clearing mucus effectively. 

What we will cover in this article 

• The primary causes of structural airway damage in the lungs 

• How severe childhood infections can lead to long-term issues 

• The role of genetic conditions like cystic fibrosis 

• Immune system deficiencies and their link to lung damage 

• Obstructions and other physical factors that trigger the condition 

• Why some cases are classified as idiopathic or of unknown cause 

Primary causes of bronchial widening 

The development of bronchiectasis usually stems from an initial injury to the lungs that triggers a ‘vicious cycle’ of infection and inflammation. When the bronchial tubes are damaged, they lose their ability to clear out mucus. This stagnant mucus becomes infected, which causes further inflammation and more damage to the airway walls, eventually leading to permanent widening. 

• Infection-led damage: Repeated bouts of pneumonia or severe bronchitis. 

• Inflammatory response: The body’s own defence system can inadvertently scar lung tissue during a heavy infection. 

• Ciliary failure: Damage to the tiny hairs that move mucus out of the lungs. 

• Tissue scarring: Fibrosis or scarring that pulls the airways open. 

Cause Category	Example Conditions	Impact on Airways
Post-infectious	Whooping cough, Measles	Direct scarring of the bronchial wall
Genetic	Cystic Fibrosis, PCD	Thick mucus or poor clearance
Immune Deficiency	Hypogammaglobulinaemia	Frequent, unhindered lung infections
Obstruction	Inhaled object, Tumour	Mucus build-up behind the blockage

The role of severe childhood infections 

Historically, many cases of bronchiectasis in the UK were the result of severe infections during childhood. While vaccinations have made these less common, some individuals still develop the condition following a particularly aggressive lower respiratory tract infection. If the lungs are damaged during their development phase, the structural changes can become a lifelong issue. 

• Whooping Cough (Pertussis): Can cause significant airway inflammation in young children. 

• Measles: In some cases, this can lead to severe pneumonia that scars the bronchi. 

• Tuberculosis (TB): A bacterial infection that can leave permanent cavities or widened tubes. 

• Severe Pneumonia: Any infection that causes deep tissue damage in the lungs. 

Genetic and congenital conditions 

For many people, bronchiectasis is linked to an underlying genetic factor that affects how the lungs handle mucus or fight off bacteria. These conditions often mean that the individual is born with a predisposition to lung damage because their natural clearing mechanisms are faulty from the start. 

• Cystic Fibrosis: The most well-known cause, where thick, sticky mucus clogs the airways. 

• Primary Ciliary Dyskinesia (PCD): A condition where the cilia do not move correctly to clear mucus. 

• Alpha-1 Antitrypsin Deficiency: A protein deficiency that can lead to lung and liver damage. 

• Congenital defects: Rare instances where the bronchial tubes do not develop correctly in the womb. 

Immune system deficiencies 

A healthy immune system is vital for keeping the lungs clear of harmful bacteria. If a person has an underlying immune deficiency, they may experience frequent ‘silent’ or overt infections that slowly erode the integrity of the bronchial walls. Over several years, these repeated minor injuries accumulate into the permanent widening known as bronchiectasis. 

• Antibody Deficiencies: Low levels of protective proteins in the blood. 

• Autoimmune Diseases: Conditions like rheumatoid arthritis or Crohn’s disease can sometimes affect the lungs. 

• Secondary Weakness: Immune suppression due to medical treatments or other chronic illnesses. 

Physical obstructions and aspiration 

Sometimes the cause of bronchiectasis is purely mechanical. If a foreign object is inhaled and becomes stuck in a bronchial tube, or if a growth like a tumour blocks an airway, mucus will pool behind the obstruction. This pooled mucus quickly becomes infected, damaging the specific section of the lung located behind the blockage. 

• Inhaled Objects: Small pieces of food or plastic, often occurring in childhood. 

• Tumours: Both benign and malignant growths can block airflow. 

• Aspiration: Regularly inhaling stomach acid or food particles due to swallowing difficulties (dysphagia). 

Idiopathic bronchiectasis: The unknown cause 

In roughly half of all cases diagnosed in the UK, a specific underlying cause cannot be found despite extensive testing. This is referred to as idiopathic bronchiectasis. While the cause is unknown, the management of the condition remains the same, focusing on clearing the lungs and preventing further infections. 

• Clinical tests may show healthy immune systems and no genetic markers. 

• It is possible that a long-forgotten childhood illness was the original trigger. 

• Research continues to look into environmental factors and subtle immune variations. 

To Summarise 

Bronchiectasis is caused by permanent damage to the bronchial tubes, often resulting from a combination of severe infections, genetic predispositions, or immune system issues. This damage creates a cycle where mucus cannot be cleared, leading to further infections and worsening airway widening. Understanding the underlying cause is helpful for tailoring treatment, though many cases remain idiopathic. 

If you experience severe, sudden, or worsening symptoms, call 999 immediately. 

Authority Snapshot 

This article was written by our Medical Content Team and reviewed by Dr. Stefan Petrov to ensure clinical accuracy. It provides a detailed overview of the various causes of bronchiectasis, from genetic factors to post-infectious damage, in line with UK clinical standards. Our goal is to offer clear and factual guidance to help readers understand the origins of chronic respiratory conditions. 

Dr. Stefan Petrov is a UK-trained physician with an MBBS and postgraduate certifications including Basic Life Support (BLS), Advanced Cardiac Life Support (ACLS), and the UK Medical Licensing Assessment (PLAB 1 & 2). He has hands-on experience in general medicine, surgery, anaesthesia, ophthalmology, and emergency care. Dr. Petrov has worked in both hospital wards and intensive care units, performing diagnostic and therapeutic procedures, and has contributed to medical education by creating patient-focused health content and teaching clinical skills to junior doctors.