Dental cavities are the most common disease in the world. Untreated tooth decay in permanent teeth affects roughly 2.24 billion people globally, making it the single most prevalent chronic condition on the planet. That number has remained stubbornly high for decades, even as treatments have improved in wealthier countries.
The answer depends partly on how you define “disease,” though. A cavity is a chronic condition you carry until it’s treated. The common cold produces far more total episodes each year but resolves on its own within days. Below is a look at the most widespread health conditions by different measures, so you can see the full picture.
Dental Cavities Top the List
Untreated cavities in permanent teeth affect about 2.24 billion people at any given time, with an age-standardized prevalence rate of roughly 27,500 per 100,000 people. That means more than one in four people on Earth is currently living with at least one untreated cavity. The condition is so widespread partly because cavities don’t heal on their own. Once decay starts, it stays until a dentist intervenes, so cases accumulate across entire lifetimes.
Cavities are driven by bacteria in the mouth that feed on sugars and produce acid, gradually dissolving tooth enamel. They’re more common in populations with limited access to dental care and in countries where diets have shifted toward processed, sugar-heavy foods. The sheer scale of the problem is easy to overlook because a single cavity rarely feels like a serious health crisis, but left untreated, decay leads to pain, infection, tooth loss, and difficulty eating.
Tension-Type Headaches Affect One in Three Adults
About 33% of adults aged 18 to 65 worldwide experience tension-type headaches, making them the most common neurological condition. A large meta-analysis pooling individual data from over 41,000 adults across 17 countries estimated a prevalence of 33.2%, and researchers noted this is likely an undercount because people who also have migraines weren’t always captured in the tension-type headache category. An extended diagnostic approach pushed the estimate closer to 35%.
Tension-type headaches produce a pressing, band-like sensation around the head. They’re distinct from migraines, which tend to be one-sided and pulsing. Most episodes are mild to moderate and don’t prevent daily activities, which is precisely why they’re underreported. Many people never mention them to a doctor.
Hypertension: 1.4 Billion and Growing
An estimated 1.4 billion adults aged 30 to 79 had high blood pressure worldwide in 2024. What makes hypertension especially concerning is the gap between who has it and who knows: roughly 600 million of those people, about 44%, are unaware of their condition. High blood pressure causes no obvious symptoms for years, but it quietly damages blood vessels, the heart, kidneys, and brain. It’s the leading risk factor for heart disease and stroke, which together are the world’s top causes of death.
This is where the distinction between common and deadly matters. Dental cavities affect more people, but hypertension kills far more. A condition can rank low on the “most widespread” list and still be among the most dangerous, which is why public health experts track prevalence and mortality separately.
The Common Cold by Volume
If you count total episodes rather than how many people are living with a condition at one time, the common cold dominates. Adults in the United States average two to three colds per year, and children get even more. Scaled globally across 8 billion people, that translates to billions of individual infections annually. But because each cold resolves within a week or two, the number of people sick at any single moment is much smaller than the number carrying untreated cavities or high blood pressure.
This is the key distinction in how epidemiologists measure disease. Prevalence counts everyone currently affected. Incidence counts new cases over a period. The common cold has extraordinary incidence but relatively low point prevalence, while dental cavities have enormous prevalence because they persist indefinitely without treatment.
Other Conditions With Massive Reach
Iron Deficiency Anemia
Iron deficiency is the most common nutritional deficiency in the world, and it’s the primary driver of anemia. About 539 million non-pregnant women aged 15 to 49 and 269 million young children are anemic globally. Among pregnant women, the rate is 37%. Anemia reduces the blood’s ability to carry oxygen, causing fatigue, weakness, and difficulty concentrating. In children, it can impair cognitive development. Inadequate dietary iron intake is the leading cause, though malaria and inherited blood disorders also contribute significantly in certain regions.
Depression
An estimated 4% of the global population lives with depression, with the rate rising to 5.7% among adults. Women are affected more often than men (6.9% versus 4.6%), and adults over 70 have a prevalence of 5.9%. In raw numbers, that translates to hundreds of millions of people. Depression often coexists with anxiety, chronic pain, and other conditions, compounding its impact on daily life.
Acne
Acne affects roughly 9.8% of adolescents and young adults aged 10 to 24, and the rate has been climbing. In 1990, the age-standardized prevalence among this age group was about 8,563 per 100,000 people. By 2021, it had risen to 9,791 per 100,000. Teenagers aged 15 to 19 have the highest rates. While acne is rarely dangerous, it can cause lasting scarring and significant psychological distress during formative years.
Vision Problems
More than 800 million people have near-vision impairment (presbyopia) that could be corrected with a simple pair of reading glasses. Uncorrected refractive errors, including nearsightedness, farsightedness, and astigmatism, are the leading cause of vision impairment worldwide. These aren’t diseases in the traditional sense, but they represent a massive, often easily solvable burden on quality of life.
Most Common vs. Most Deadly
The most common diseases and the deadliest diseases are almost entirely different lists. Heart disease and stroke kill more people than anything else, but their prevalence is far lower than dental cavities or headaches. Conversely, cavities affect billions of people but directly cause very few deaths. Understanding this split matters because public health funding, media attention, and personal worry don’t always align with the actual numbers. Conditions like untreated cavities and iron deficiency affect staggering numbers of people, particularly in lower-income countries, but attract a fraction of the attention given to rarer but more dramatic diseases.
The bottom line: dental cavities are the most common disease measured by how many people are currently living with the condition. If you broaden the question to include all health conditions, tension-type headaches and hypertension are close behind, each affecting over a billion people worldwide.