20th century

==== Notable diseases ====
* An [[influenza]] pandemic, [[1918 flu pandemic|Spanish Flu]], killed anywhere from 17 to 100 million people between 1918 and 1919.
* A new [[virus|viral]] disease, called the [[Human Immunodeficiency Virus]], or HIV, arose in Africa and subsequently killed millions of people throughout the world. HIV leads to a syndrome called [[Acquired Immunodeficiency Syndrome]], or AIDS. Treatments for HIV remained inaccessible to many people living with AIDS and HIV in [[developing countries]], and a cure has yet to be discovered.
* Because of increased [[Life expectancy|life spans]], the [[prevalence]] of cancer, [[Alzheimer's disease]], [[Parkinson's disease]], and other diseases of [[old age]] increased slightly.
* Changes in food production, along with [[sedentary lifestyle]]s due to labor-saving devices and the increase in home entertainment, contributed to an "epidemic" of [[obesity]], at first in the rich countries, but by the end of the 20th century spreading to the developing world.