What causes tuberculosis?Â
Tuberculosis is caused by an infection with a type of bacterium called Mycobacterium tuberculosis. Unlike many other common infections, it is not spread through touch, surface contact, or sharing food and drink. Instead, it is an airborne condition, meaning the bacteria are released into the air when a person with an active infection in their lungs or throat coughs, sneezes, speaks, or sings.
What We’ll Discuss in This ArticleÂ
- The specific bacterium responsible for the infection.Â
- How the bacteria are transmitted from person to person.Â
- The difference between exposure and developing the disease.Â
- Environmental factors that facilitate the spread of TB.Â
- Health conditions that increase the risk of infection.Â
- The biological process of the bacteria entering the body.Â
The primary bacterial causeÂ
The sole cause of tuberculosis is the Mycobacterium tuberculosis bacterium. These bacteria are particularly hardy because they have a thick, waxy cell wall that protects them from the body’s immune system and certain types of antibiotics. While there are other species of mycobacteria that can cause illness in animals, the vast majority of human TB cases in the UK are caused by this specific human strain. The NHS explains that while the bacteria usually attack the lungs, they can travel through the bloodstream to any part of the body.
How the infection spreadsÂ
Tuberculosis is transmitted through the air in microscopic droplets. When an individual with active pulmonary TB (TB in the lungs) coughs or sneezes, they expel these tiny droplets containing the bacteria. If another person breathes in these droplets, the bacteria can settle in their lungs and begin to grow. It usually requires prolonged or frequent close contact with an infectious person to catch the disease. For this reason, most people are infected by someone they live or work with rather than by a stranger on public transport.
From inhalation to infectionÂ
Once the bacteria are inhaled, they travel down the airways to the small air sacs in the lungs called alveoli. At this stage, the body’s immune system typically responds by surrounding the bacteria with immune cells to form a “wall” around them. This results in latent TB, where the bacteria are alive but inactive. NICE guidelines on tuberculosis management highlight that only a small percentage of people who breathe in the bacteria will actually develop active symptoms immediately. Most people’s immune systems are strong enough to keep the bacteria dormant for many years.
Factors that increase susceptibilityÂ
While the bacteria are the direct cause, certain factors make it much more likely for an individual to become ill after exposure. A weakened immune system is the most significant risk factor, as it may be unable to contain the bacteria. This includes people living with HIV, those undergoing chemotherapy, or individuals taking long-term steroid medications. Lifestyle factors and living conditions also play a role, as the bacteria thrive in poorly ventilated or overcrowded environments where air circulation is limited.
Latent TB reactivationÂ
In many cases, the “cause” of an active TB case is actually the reactivation of a dormant infection that the person has carried for years. This is known as secondary TB. This reactivation usually occurs when the person’s health declines due to age, malnutrition, or the onset of another illness. Because the bacteria can remain “asleep” in the body for a lifetime, many people are unaware they are carrying the cause of the disease until their immune system can no longer keep it under control.
ConclusionÂ
Tuberculosis is caused by a specific bacterial pathogen that spreads through the air during close contact. Understanding that it is an airborne infection helps in implementing the correct preventative measures, such as proper ventilation and the use of masks in high-risk settings. Most healthy individuals who are exposed will not become ill immediately, but they may carry the bacteria in a latent state. If you experience a sudden onset of a very high fever, a stiff neck, or a severe headache, call 999 immediately.
Can you get TB from a blood transfusion?Â
No, tuberculosis is not spread through blood contact. It is strictly an airborne infection that enters the body through the respiratory system.Â
Is TB caused by cold weather or damp housing?
Cold weather and dampness do not cause TB, as only the specific bacteria can do that. However, overcrowded and poorly ventilated housing can make it much easier for the bacteria to spread from person to person.Â
Why do only some people get sick after breathing in the bacteria?Â
The immune system is often able to kill or wall off the bacteria. Whether you get sick depends on the strength of your immune response and the amount of bacteria you inhaled.Â
Can animals give tuberculosis to humans?Â
A specific type called Mycobacterium bovis can be found in cattle and passed to humans through unpasteurised milk, though this is now very rare in the UK due to milk pasteurisation and cattle testing.Â
Does smoking cause tuberculosis?Â
Smoking does not cause TB, but it significantly increases the risk of catching it and makes the infection much harder for the body to fight off because it damages the lungs.Â
How long can TB bacteria stay alive in the air?Â
In a closed, unventilated room, the tiny droplets can remain suspended in the air for several hours after an infectious person has left.Â
Can I catch TB from a surface like a doorknob?Â
No, the bacteria do not survive well on hard surfaces and are not transmitted through skin contact or “fomites” like handles or clothes.Â
Authority Snapshot (E-E-A-T Block)Â
This article outlines the biological and environmental causes of tuberculosis based on established UK medical standards. The content is curated and reviewed by a team of UK-trained physicians to ensure it adheres to current NHS and NICE clinical frameworks. Our aim is to provide the public with clear, factual, and safe information regarding the transmission and risks of bacterial infections.
