Tuberculosis spreads through the air when a person with infectious TB disease of the lungs or throat releases germs that another person breathes in. Speaking, coughing and singing can release them. Inactive TB, also called latent TB infection, cannot spread to other people. The distinction between infection and infectious disease is essential when discussing risk at home, school or work.
TB is caused by bacteria called Mycobacterium tuberculosis. It most often affects the lungs, although it can affect other parts of the body. This explainer uses public guidance from WHO and the US Centers for Disease Control and Prevention to describe transmission. It does not diagnose TB or recommend a treatment or medicine.
| Situation | What official guidance says |
|---|---|
| Infectious TB in the lungs or throat | Germs can pass through shared air. |
| Inactive or latent TB infection | The person cannot spread TB germs. |
| Indoor space with poor air circulation | Transmission is more likely than outdoors. |
| Shaking hands or touching toilet seats | These are not ways TB germs spread. |
How does tuberculosis spread from one person to another?
The CDC explanation of TB causes and transmission says germs can enter the air when someone with active TB disease of the lungs or throat coughs, speaks or sings. Depending on the environment, they can remain in the air for several hours. Someone nearby can breathe them in and become infected.
The WHO tuberculosis questions and answers page likewise identifies airborne spread. It explains that people with lung TB can release germs while breathing, speaking, coughing, sneezing or spitting. Transmission therefore should not be imagined only as a visible cough directly onto another person.
Air circulation and the setting matter. CDC says spread is more likely indoors or in places with poor air circulation than outdoors. People with active TB disease are most likely to spread it to people they spend time with regularly, including family members, friends, colleagues and classmates. A shared room over time is a different exposure situation from simply knowing someone's name or diagnosis.
This does not produce a universal safe distance or a fixed number of minutes after which everyone becomes infected. The public pages do not provide such a rule for all environments. Avoid turning a general description into a personal risk calculation without a health professional's assessment of the actual circumstances.
Can sharing food or touching surfaces spread TB?
CDC specifically says TB germs do not spread by shaking someone's hand, sharing food or drink, touching bed linen or toilet seats, sharing toothbrushes, or kissing. These statements describe the transmission route for TB. They should not be interpreted as general hygiene advice about other infections.
The distinction can prevent a common misunderstanding in households. If two people share a meal in a poorly ventilated room with someone who has infectious lung TB, the relevant TB concern is the shared air, not the food itself. This is an illustration of the airborne route, not an assessment of any particular family's exposure.
It also means that excluding a person because they have a history of TB or refusing ordinary social contact on the basis of a label does not explain present infectiousness. A clinical assessment determines the person's condition and the precautions needed. Rumours about contaminated belongings can distract from the actual route of spread.
What is the difference between inactive TB and TB disease?
TB bacteria can remain in the body without causing active disease. CDC calls this inactive TB or latent TB infection. People with inactive TB do not feel sick from it, have no symptoms of TB disease and cannot spread the germs to others. Infection does not automatically mean that someone is currently infectious.
However, inactive infection can later develop into active disease. WHO explains that most people infected with TB bacteria do not have TB disease, while people with compromised immune systems face a higher risk of developing it. Health conditions such as HIV and diabetes are among the factors WHO identifies. Individual risk needs medical assessment.
Do not reverse these statements and assume that a person who looks well must have inactive infection. WHO says some people with TB disease have mild symptoms or none at all, which can delay recognition and allow continued spread. Feeling well cannot establish the category. Equally, a cough alone does not establish that someone has TB.
The site of disease also matters. CDC says active TB disease of the lungs or throat can be infectious, while disease in places such as the kidney or spine is usually not infectious. The word usually matters here: a general explainer cannot determine the precautions appropriate to an individual case.
What should you do after possible TB exposure?
CDC advises contacting a health care provider if you think you have spent time with someone who has active TB disease. Tell the clinician when the contact happened and describe the setting. That information helps the professional decide what assessment is appropriate. Do not assume that every contact has become infected or that an online symptom list can settle the question.
If you have an existing health condition, consult a qualified doctor about possible exposure and your individual risk. Decisions about testing, infectiousness, attendance at school or work, and any care needed belong with the treating health team. There is no single self declared return date that follows from the information in this article.
For related reading, see our guides to antibiotic resistance, breathing changes that need attention in children and hand washing technique. Those topics address different questions. For TB transmission, keep attention on shared air, the clinical distinction between inactive infection and disease, and qualified assessment after a possible exposure.
