Tuberculosis (TB) in humans is caused by a specific bacterium called Mycobacterium tuberculosis , which spreads through the air when someone with active TB in their lungs coughs, talks, laughs, sings, or sneezes near others. The germ usually enters through the lungs, can stay “silent” for years, and may later become active if the immune system becomes weak.

What directly causes TB?

  • The immediate cause of TB is infection with the bacterium Mycobacterium tuberculosis.
  • When an infected person with active lung or throat TB releases tiny droplets into the air, another person can inhale these and become infected.
  • After being breathed in, the bacteria settle in the lungs first, then can spread via the bloodstream to places like the kidneys, spine, or brain.

In simple terms: TB starts when TB bacteria in the air are breathed into the lungs and manage to survive and multiply instead of being cleared by the immune system.

How does TB spread between people?

  • TB spreads through the air , not by shaking hands, sharing food, or touching surfaces.
  • The risk is highest with close, prolonged contact (for example, living in the same household) with someone who has active, untreated TB in the lungs or voice box.
  • People with latent TB infection (bacteria in the body but no symptoms) do not spread TB to others.

Why do some people get sick and others don’t?

Most people who breathe in TB bacteria either kill the germs or keep them under control as latent TB infection. TB becomes active disease when the immune system can no longer hold the bacteria in check.

Key factors that make active TB more likely include:

  • Weak immune system
    • HIV infection or AIDS
    • Cancer or chemotherapy
    • Medications that suppress immunity (after organ transplant, for autoimmune diseases like lupus or rheumatoid arthritis)
    • Long-term steroid use
  • Chronic health conditions
    • Diabetes
    • Severe kidney disease
    • Some cancers (especially of the head, neck, blood)
  • Lifestyle and nutritional factors
    • Malnutrition or very low body weight
    • Heavy alcohol use
    • Smoking or other tobacco use
    • Use of injected or other illicit drugs
  • Age and general vulnerability
    • Young children, especially under 5 years, and very elderly people have less robust immunity.

Environmental and living conditions

Beyond the germ itself, certain living conditions make TB infection and TB disease more likely to occur and to spread:

  • Crowded housing, poor ventilation, prisons, shelters, or other closed settings.
  • Air pollution and regular exposure to smoke or dust (for example, from certain jobs) can weaken lung defenses.
  • Living or working in areas where TB is common increases the chance of repeated exposure.

These conditions do not “create” TB; they increase the chance that TB bacteria will spread and that infection will progress to active disease.

Quick Scoop (forum-style take)

If someone in a forum asks “what causes TB in humans,” the core points usually boil down to:

  1. Main cause
    • A specific bacterium, Mycobacterium tuberculosis , is the root cause of TB in humans.
  1. How you actually catch it
    • Breathing in air that contains TB bacteria from a person with active lung or throat TB who is coughing, speaking, or even singing near you over time.
  1. Why some people get really sick
    • A weak or stressed immune system (HIV, diabetes, cancer treatment, malnutrition, heavy alcohol use, smoking, certain medications) lets the bacteria break out of “silent” mode and cause full-blown TB disease.
  1. What doesn’t cause TB
    • TB is not caused by curses, cold weather, or casual contact like hugging or sharing utensils; the bacterium plus inhaled droplets plus time and vulnerability are what matter.

TL;DR: TB in humans is caused by infection with Mycobacterium tuberculosis bacteria, which spread through the air from people with active lung or throat TB; whether someone develops active disease depends heavily on their immune strength, health conditions, and living environment.

Information gathered from public forums or data available on the internet and portrayed here.