Certain pathogens, like viruses and bacteria, can cause long-term inflammation or directly damage DNA in ways that eventually lead to cancer.

For example, hepatitis B and C viruses are key drivers of liver cancer. Some types of the human papillomavirus are responsible for cervical cancer. The bacterium H. pylori can cause stomach ulcers and cancers.

The International Agency for Research on Cancer estimates that around 13% of cancers overall are directly caused by infections, as the chart shows.

For some cancer types, they estimate that infections cause nearly all cases. They’re listed at the top of the chart and include cervical cancer, adult T-cell leukemia and lymphoma, and non-cardia stomach cancer.

This is an area where prevention can be very powerful: by tackling the infections that cause them, we can stop these cancers before they start.

Vaccines for human papillomavirus and hepatitis B have already been developed and have lowered cancer rates in younger generations. Additionally, antibiotics for H. pylori, antiviral treatments, and improved hygiene can dramatically reduce the risks of other infections.

I recently wrote an article about the virus that causes cervical cancer and how vaccines can eliminate it. You can read it here →

There are considerable differences in access to healthcare across the world.

Rich countries have around ten times as many doctors per person as poor countries. You can see this in this chart, which shows the number of medical doctors per 1,000 people in a population. This includes generalist physicians as well as specialists.

The global average is around 1.7 doctors per 1,000. In low-income countries, the figure is around five times lower.

Explore more data on healthcare spending and access →

Homicide rates measure the number of intentional, illegal killings per 100,000 people annually.

Since 2000, rates in the United States have fluctuated around 6 homicides per 100,000. They fell from a peak of 6.7 in 2001 to 4.4 in 2014 but climbed back to 6.4 in 2022. Preliminary data suggests they fell back to 5.7 in 2023.

Over the same period, Europe’s rates fell from nearly 8 per 100,000 people in 2000 to just above 2 — a drop of almost three-quarters.

Explore homicide rates in many more countries →

In some countries such as Japan, the United States, or South Korea, almost all households have air conditioning in their homes. In others, almost none do. This includes countries like India or South Africa where extreme heat is frequent.

In this chart, you can see the share of households that had air conditioning (AC) in 2018. This data comes from the International Energy Agency.

Paying for the upfront cost of an AC unit is a key barrier to adoption, so as incomes rise, more people get access to them.

Access to air conditioning is becoming increasingly important as the world warms and extreme heat becomes more common.

Read more about how populations can protect themselves against extreme heat →

Cancer death rates rise steeply with age.

The chart shows this for a wide range of cancers, including bladder, breast, colorectal, stomach, and prostate cancer. The data comes from the United States Centers for Disease Control and Prevention.

Long-term exposure to risk factors — such as smoking, radiation, and certain infections — damages our cells. This damage accumulates with age, increasing the chances of cancerous mutations. In addition, our cells’ ability to repair this damage also weakens, allowing the mutations to accumulate.

Cervical cancer has a slightly different shape: its risks rise at a much younger age and then slow down. This is because it is caused by the human papillomavirus (HPV), typically spread through sexual contact at younger ages. Without HPV, it’s very rare for this cancer to develop, and infection can be prevented with early vaccination.

Read more about the risks of cancer with age →

Demographic trends, such as births and deaths, can be influenced by many factors. Wars or pandemics can lead to higher death rates, while lower child mortality and access to contraception reduce the number of births.

But specific cultural beliefs can also have a strong effect, as in Japan in 1966. As you can see in the chart, the UN estimates that births decreased by about 20% from 1965 to 1966.

The reason behind this drop is unusual. Children born in 1966 had the “fire horse” as their birth sign. According to astrological predictions, women born that year would bring bad fortune, especially for their future husbands.

Families who either believed this, or wanted to avoid the risk of their daughters having difficulty in the marriage market, chose not to have children that year. Couples may have abstained or used contraception, and in addition, the induced abortion rate in 1966 was significantly higher than in the surrounding years.

The next year of the fire horse is 2026. With the decline of these beliefs in Japan, fewer arranged marriages (where the birth sign might be a significant factor), and generally declining birth rates, we are unlikely to see this sharp drop in births again.

Explore more data on births and fertility in our Population & Demography explorer →

On average, Europeans consume more dairy products than people in other regions.

This chart shows the milk supply per person in each of the world’s regions. This is based on data from the Food and Agriculture Organization of the United Nations. It’s based on supply — the amount of milk available for consumption. It includes consumer waste, so it is a bit higher than the amount that is consumed in the end.

As you can see, the per-capita supply for Europe is more than twice the global average. People across Africa and Asia consume far less.

These numbers include dairy products such as yogurt and cheese, based on how much milk is used to produce them.

Explore country-by-country data on milk supply →