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The 20th century saw major progress in the fight against disease, as understanding of what causes illness and disease grew.

However, some diseases still pose a challenge to scientists, particularly cancers and certain bacterial and viral diseases. These can be either difficult or impossible to treat and cure. Additionally, even when the causes and treatments for diseases are well known, problems can develop when individuals do not take the right steps to either prevent disease or reduce risk to themselves.

In the early 21st century, most of the dreaded diseases of a century ago no longer cause many deaths. For example, smallpox has been wiped out in Britain and improved sanitation has resulted in typhus no longer being found.

However, people are living longer in the 21st century than in the past. As a result, their chances of developing illnesses like cancer or heart disease within their lifetime have increased. People’s lifestyle choices and environmental factors can also increase their risk of getting one of these medical conditions.

Lifestyle

Illness can be caused by the type of life a person leads, such as whether a person smokes, eats a poor diet or drinks too much alcohol. These choices can lead to a wide range of problems, such as heart issues, cancers, obesity and diabetes. This has been the case throughout history. However, it is only in the past 100 years that a scientific link has been made between lifestyle and some illnesses.

Environmental factors

Problems such as pollution and or work-related issues, eg stress or long working hours, are also potential causes of illness.

Wars, epidemics and famines

War, epidemics and famines killed more people in the 20th century than in any other period of history.

Famine no longer poses a threat in more developed countries, such as the UK. However, it is still a major issue facing many developing countries around the world.