More than 36 million U.S. adults smoke cigarettes, and a majority of those adults are of a low socioeconomic status.
A new study from the Colorado School of Public Health found nearly three-fourths of smokers have "one or more low-socioeconomic disadvantages."
The study found that about one in four adults without a high-school diploma is a smoker. And about 28 percent of people who smoke live in poverty.
Additionally, around 40 percent of Medicaid recipients and adults with disabilities are smokers.
Researchers say this can raise ethical concerns when it comes to U.S. tobacco control.
A separate study from the Centers for Disease Control and Prevention found there's a higher density of tobacco retailers in low-income neighborhoods.