20th century

=== Medicine ===
[[File:Faroe stamp 079 europe (fleming).jpg|thumb|right|A stamp commemorating [[Alexander Fleming]]. His discovery of [[penicillin]] changed the world of medicine by introducing the age of antibiotics.]]

* [[Placebo]]-[[scientific control|controlled]], [[random sample|randomized]], [[blind experiment|blinded]] [[clinical trial]]s became a powerful tool for testing new medicines.
* [[Antibiotics]] drastically reduced mortality from [[bacterial disease]]s.
* A [[vaccine]] was developed for [[polio]], ending a worldwide epidemic. Effective vaccines were also developed for a number of other serious infectious diseases, including [[influenza vaccine|influenza]], [[DPT vaccine|diphtheria, pertussis (whooping cough), tetanus]], [[MMR vaccine|measles]], [[mumps vaccine|mumps]], [[MMR vaccine|rubella (German measles)]], [[varicella vaccine|chickenpox]], [[hepatitis A vaccine|hepatitis A]], and [[hepatitis B vaccine|hepatitis B]].
* [[Epidemiology]] and [[vaccination]] led to the eradication of the [[smallpox]] virus in humans.
* [[X-ray]]s became a powerful diagnostic tool for a wide spectrum of diseases, from bone fractures to cancer. In the 1960s, [[computerized tomography]] was invented. Other important diagnostic tools developed were [[sonography]] and [[magnetic resonance imaging]].
* Development of [[vitamins]] virtually eliminated [[scurvy]] and other vitamin-deficiency diseases from industrialized societies.
* New psychiatric drugs were developed. These include [[antipsychotic]]s for treating [[hallucination]]s and [[delusion]]s, and [[antidepressant]]s for treating depression.
* The role of [[tobacco smoking]] in the causation of cancer and other diseases was proven during the 1950s (see [[British Doctors Study]]).
* New methods for cancer treatment, including [[chemotherapy]], [[radiation therapy]], and [[immunotherapy]], were developed. As a result, cancer could often be [[cure]]d or placed in [[remission (medicine)|remission]].
* The development of [[blood type|blood typing]] and [[blood bank]]ing made [[blood transfusion]] safe and widely available.
* The [[invention]] and development of [[immunosuppressive drug]]s and [[tissue typing]] made [[organ transplant|organ and tissue transplantation]] a clinical reality.
* New methods for [[heart surgery]] were developed, including [[pacemaker]]s and [[artificial heart]]s.
* [[Cocaine]] and heroin were widely illegalized after being found to be addictive and destructive. [[Psychoactive drug]]s such as [[LSD]] and [[MDMA]] were discovered and subsequently prohibited in many countries. [[Prohibition of drugs]] caused a growth in the black market drug industry, and [[War on drugs|expanded enforcement]] led to a larger prison population in some countries.<ref>{{Cite web|last=Engel|first=Pamela|date=April 23, 2014|title=Watch How Quickly The War On Drugs Changed America's Prison Population|url=https://www.businessinsider.com/how-the-war-on-drugs-changed-americas-prison-population-2014-4?op=1|website=Business Insider}}</ref>
* [[Contraceptive]] drugs were developed, which reduced population growth rates in industrialized countries, as well as decreased the taboo of [[premarital sex]] throughout many western countries.
* The development of medical [[insulin]] during the 1920s helped raise the life expectancy of [[diabetes|diabetics]] to three times of what it had been earlier.
* Vaccines, hygiene and clean water improved health and decreased mortality rates, especially among infants and the young.

==== 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.