Why Life Expectancy Skyrocketed in Early 20th-Century America

Before the widespread acceptance of germ theory in the late 1800s, the medical community had limited understanding of how diseases spread. Public health crises, including epidemics of cholera and typhus fever, were common and unrelenting, especially in large cities where rapid industrialization and urbanization led to overcrowding and poor sanitary conditions.

From 1850 to 1880, the annual U.S. life expectancy at birth hovered around 40 years, with a sharp dip in the early 1860s due to the Civil War. However, that figure was heavily skewed by high early-age mortality, says S. Jay Olshansky, professor of public health at the University of Illinois Chicago. From the mid- to late 1800s, roughly 30 to 40 percent of children in the United States died before the age of five.

Dubbed the “Sanitary Revolution” in the United States and beyond, the period around the turn of the 20th century witnessed major breakthroughs in medicine and public health. According to the Centers for Disease Control and Prevention (CDC), life expectancy in the United States rose to 47.3 years by 1900 and 68.2 years by 1950—rapid increases driven primarily by saving the young, Olshansky says.

In the mid-19th century, human mortality was basically in the grip of natural forces, says Samuel Preston, emeritus professor of sociology at the University of Pennsylvania. The largely unregulated medical field was slow to advance due to a lack of understanding of disease and limited technology. 

“There was little gain to be had from medicine,” says Preston, co-author of Fatal Years: Child Mortality in Late Nineteenth-Century America. The exception was the smallpox vaccination, introduced in the late 1700s and widely used by the 1840s and ’50s. According to Preston, child mortality rates were significantly higher in large cities than in smaller cities and rural areas and among the Black (often enslaved) population compared with white people.

Communicable diseases—from tuberculosis to pneumonia—were often to blame for child deaths. The prevailing miasma theory at the time suggested that airborne pollutants from foul odors and unsanitary conditions caused these illnesses. That started to change after French scientist Louis Pasteur first published his germ theory findings in 1861. The subsequent work of Pasteur and other scientists led to greater acceptance by the late 1800s that microorganisms, including bacteria, caused disease. 

Equipped with a newfound understanding of the link between bacterial contamination and disease, the medical community helped inform public health on how to manage water, sewage and controlling epidemics, says Michael Haines, economics professor at Colgate University, who co-authored Fatal Years with Preston.

Many metropolitan cities modernized water filtration and distribution methods beginning in the late 1800s, and state and local health departments started regulating water quality and sewage practices. As flush toilets replaced outhouses, most New York City neighborhoods had sewer service by 1902.

Greater access to indoor living and working environments helped combat the spread of disease, according to Olshansky. So did innovations in food preparation, including refrigeration and, for cooking, cast-iron stoves and gas ovens. American households learned about germ theory through public health campaigns, consumer advertisements for sanitary goods, child care manuals and the domestic science movement.

“Boiling of water and milk was a practice that was unknown until the 1890s,” Preston says. “Handwashing was promoted. Isolating sick patients in households was promoted. There was tremendous enthusiasm.”

Medical care was also advancing. A diphtheria antitoxin introduced in the 1890s became the first effective treatment for a deadly disease known to affect young children. The development of vaccines for a range of diseases was underway by the turn of the century. U.S. medical schools also underwent vast reforms in the early 1900s and adopted standardized, science-based curricula. Substandard proprietary schools were forced to close.

“It was [addressing] some of these basic public health issues, combined with medicine, that had a pretty dramatic effect,” Olshansky says.

As parents learned to protect their children from disease, child mortality rates fell from about 347.5 deaths per 1,000 live births in 1880 to nearly 180 deaths per 1,000 live births in 1915, according to United Nations data.

“Once we gained control over those early deaths, which began in about the latter part of the 19th century, then you start to see a dramatic increase in life expectancy,” Olshansky says. “Babies that would have died were saved by medical technology and basic public health.”

Annual U.S. life expectancy dropped during the Spanish flu pandemic of 1918-19. However, as medical science continued to advance, it increased from 47.3 in 1900 to 59.7 by 1930. Though declining child mortality rates were the leading factor, infectious diseases were also falling among most age groups, albeit at varying rates, and people began living longer.

Haines describes increasing human longevity as “one of the great achievements of the modern era.” Life expectancy was nearly 77 years by the turn of the 21st century and, since 2023, has increased to 78.4 years, according to the CDC data.

According to Olshansky, a sharp rise in life expectancy like the United States experienced in the late 1800s is likely a singular event.

“Humans 140 to 150 years ago experienced this—subsequent generations, of course, benefitted from it,” Olshansky says. “But a quantum leap in life expectancy like that can only happen once."