Roughly one in three people worldwide inhaled secondhand smoke in 2023.
A new Lancet Public Health analysis links that exposure to about 1.66 million premature deaths in 2023, with heart disease topping the list.
The study, published September 7, 2026, is the first dedicated global tally by the Institute for Health Metrics and Evaluation to isolate secondhand smoke as its own risk factor.
Researchers analyzed data from 204 countries and territories between 1990 and 2023.
Also read: Do fish oil supplements actually work? Here's what the evidence says
For US nonsmokers, the numbers make an old warning fresh.
The CDC estimates that secondhand smoke causes nearly 34,000 heart disease deaths and more than 7,300 lung cancer deaths every year among American adults who don't smoke themselves.
It is also one of the exposures behind the roughly 1 in 5 US lung cancer deaths that hit a never-smoker.
The reach hasn't shrunk as much as smoking has
Age-standardized exposure fell by about 22% globally between 1990 and 2023, the researchers found. Yet the raw headcount barely moved.
Also read: 23 dead as West Nile spreads through 40 US states: the 7 symptoms to watch for
Population growth in sub-Saharan Africa, North Africa and the Middle East kept absolute exposure roughly flat even as smoking rates dropped in wealthier countries.
Among those exposed in 2023 were 767 million children under 15. In that age group, the study linked secondhand smoke to an estimated 5.2 million respiratory infections in a single year.
Why the smoke you breathe hits harder
Most of what a nonsmoker inhales isn't the puff a smoker exhales. It's sidestream smoke, the plume drifting off the burning tip of a cigarette between drags.
That smoke is unfiltered. Per unit, it carries higher concentrations of toxic and carcinogenic compounds than the smoke pulled through the cigarette's filter.
Also read: How drinking beet juice regularly may affect your blood pressure
For adults, the CDC puts the health cost at a 25 to 30% rise in coronary heart disease risk, a 20 to 30% rise in stroke risk, and a 20 to 30% rise in lung cancer risk. Its bottom line has not shifted.
What US nonsmokers can actually do
The single most effective step is a fully smoke-free home and car.
Opening a window, running a fan or confining smoking to one room does not remove the fine particles, which hang in indoor air and settle onto furniture and clothing.
Anyone with long-standing exposure at home or in a shared workplace can raise the topic with a primary-care doctor, particularly for a baseline check on blood pressure, heart function and lung health.
Also read: Women who stay fit in midlife may cut their dementia risk by nearly 90%
Children with recurrent asthma flares or repeated ear infections deserve a look at what they're breathing indoors. Removing an in-home smoker often improves those symptoms within weeks.
CDC data through 2014 showed about 1 in 4 US nonsmokers, roughly 58 million people, were still regularly exposed to secondhand smoke.
Also read: Your metabolism may not be why you gain weight after 40 - here is the real reason
This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.