The 20th and 21st centuries

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

However, some diseases still pose a challenge to scientists, particularly cancers and bacterial and viral diseases.

Even when the causes of disease are known, individuals do not always take the right steps to prevent disease or to reduce risk.

In the early 21st century, most of the dreaded diseases of a century ago no longer cause many deaths. The major…