Tuberculosis (TB) is a bacterial infection that primarily attacks the lungs, causing a persistent cough lasting three weeks or longer, night sweats, unexplained weight loss, and fever. An estimated 10.8 million new cases and 1.25 million deaths occur worldwide each year. But not everyone infected with the TB bacteria actually feels sick, and understanding the difference between a silent infection and active disease is key to recognizing when symptoms matter.
Latent TB vs. Active TB Disease
When TB bacteria enter your body, your immune system can often wall them off and keep them dormant. This is called latent TB infection. You won’t feel sick, you won’t have symptoms, and you can’t spread it to anyone else. The only sign is a positive result on a TB skin test or blood test. Roughly a quarter of the world’s population carries latent TB.
Active TB disease is what happens when those bacteria break free and start multiplying. This is when symptoms appear, and when you become contagious. The shift from latent infection to active disease typically happens within 3 to 9 months of exposure, though it can take up to two years. In some people, it doesn’t happen at all. A weakened immune system, whether from HIV, diabetes, malnutrition, or medications that suppress immunity, significantly raises the risk of latent TB progressing to active disease.
The Hallmark Lung Symptoms
Since TB most commonly targets the lungs (pulmonary TB), the symptoms center on your respiratory system:
- A cough lasting three weeks or longer, often producing mucus or sputum
- Coughing up blood (hemoptysis), which can range from streaks in your sputum to more significant bleeding
- Chest pain, particularly when breathing deeply or coughing
- Shortness of breath that worsens as lung tissue becomes more damaged
The cough is the symptom most people notice first. It often starts dry and gradually becomes productive, bringing up thicker sputum over weeks. Because these symptoms overlap with bronchitis, pneumonia, and even lung cancer, a cough that doesn’t resolve after three weeks is the threshold that should prompt TB testing, especially if you have other risk factors.
Whole-Body Symptoms
TB doesn’t just affect your lungs. The infection triggers a powerful immune response that produces widespread inflammation, and this is what causes the “constitutional” symptoms that often feel like a slow, relentless drain on your body.
Fever occurs in 60% to 85% of people with active TB. It tends to be low-grade and persistent rather than the high, spiking fever you’d associate with the flu. Many people don’t even realize they have a fever until it’s measured.
Night sweats are one of TB’s most distinctive features. Your body’s stress hormone, cortisol, naturally dips at night. Since cortisol helps suppress the immune response and keep fever in check, its nightly drop allows TB-related inflammation to spike while you sleep. The result is drenching sweats that can soak through sheets, not just mild dampness.
Unexplained weight loss is common and can be severe. The inflammatory molecules your immune system releases to fight TB also break down muscle protein directly, creating a wasting effect that goes beyond simply eating less. These same molecules suppress leptin, a hormone that regulates weight and appetite, creating a cycle where your body loses mass even if you try to maintain your calorie intake. Fatigue and weakness follow as muscle tissue deteriorates.
Loss of appetite compounds the weight loss. Together, these symptoms can leave you feeling exhausted, weak, and visibly thinner over the course of weeks to months.
TB Outside the Lungs
In roughly 15% to 20% of active cases, TB spreads beyond the lungs to other organs. This is called extrapulmonary TB, and the symptoms depend entirely on where the bacteria settle.
TB in the lymph nodes (most commonly in the neck) causes firm, gradually enlarging swellings that may eventually drain fluid through the skin. TB in the spine, historically known as Pott disease, leads to back pain, stiffness, and in severe cases, nerve damage or spinal deformity. TB meningitis, an infection of the membranes surrounding the brain, causes headaches, confusion, neck stiffness, and sensitivity to light. It’s the most dangerous form and can progress rapidly.
TB can also affect the kidneys, bones, joints, and abdomen. In all these cases, the whole-body symptoms like fever, night sweats, and weight loss are usually still present alongside the organ-specific problems.
Symptoms in Children
Children with TB often look different from adults. A persistent cough is still common, but the more telling signs are subtler. Children may show general weakness, reduced playfulness, or lethargy that parents initially attribute to a passing illness. Fever and night sweats occur just as in adults.
The most important red flag in young children is failure to thrive: not gaining weight or growing as expected over weeks or months. Because children, especially those under five, are more likely to develop severe forms of TB, including TB that spreads to the brain or throughout the body, these vague symptoms deserve attention if a child has been in close contact with someone who has active TB.
How TB Is Detected
TB testing typically starts with either a skin test or a blood test. For the skin test, a small amount of protein derived from TB bacteria is injected just under the skin of your forearm. You return 48 to 72 hours later so a healthcare provider can measure any raised, firm bump (induration) at the injection site.
What counts as a “positive” result depends on your risk level. For people with HIV, organ transplant recipients, or those recently exposed to someone with active TB, a bump of 5 millimeters or more is considered positive. For people born in countries where TB is common, those with diabetes or kidney disease, or children under five, the threshold is 10 millimeters. For people with no known risk factors, 15 millimeters or more is required for a positive reading.
A positive skin test or blood test tells you that you’ve been exposed to TB bacteria, but it doesn’t tell you whether you have latent infection or active disease. That distinction requires a chest X-ray and, if there are lung abnormalities, sputum samples to look for the bacteria directly.
What Treatment Looks Like
Active TB is treated with a combination of antibiotics taken for a minimum of six months, sometimes longer for drug-resistant strains or extrapulmonary disease. The first two months involve multiple medications, after which the regimen narrows for the remaining four months. Most people start feeling better within a few weeks, but stopping treatment early is dangerous: it allows surviving bacteria to develop resistance, making the disease much harder to treat.
Latent TB is also treated, though with a simpler regimen lasting three to four months, to prevent it from becoming active. Treatment for latent TB is especially important for people with weakened immune systems, recent close contacts of active TB cases, and children under five who test positive.
During treatment for active TB, you’ll typically be considered contagious for the first few weeks. Your healthcare provider will let you know when sputum tests confirm you’re no longer spreading bacteria, which usually happens within two to three weeks of starting effective treatment.