States with weaker concealed carry laws are associated with significantly higher rates of handgun homicide, according to a new study.

A new study led by a School of Public Health researcher from the Boston University School of Public Health has found that less stringent regulations about carrying concealed firearms is associated with significantly higher rates of handgun-related homicide.

The study, which was funded by the Robert Wood Johnson Foundation, was published in the American Journal of Public Health. It suggests that more permissive concealed-carry laws not only do not promote public safety, but are detrimental to it.

“Some have argued that the more armed citizens there are, the lower the firearm homicide rate will be, because the feared or actual presence of armed citizens may deter violent crime,” says lead author Michael Siegel, an SPH professor of community health sciences. “Our study findings suggest that this is not the case.”

Currently, all states allow certain people to carry a concealed handgun, but there are variations in permitting policy. Nine states have “may issue” laws, giving law enforcement officials wide discretion in issuing concealed carry permits. Police chiefs in these states can deny a permit if they deem the applicant to be at risk for violent behavior, even if there is no criminal history. In the 29 “shall issue” states, there is little or no discretion. And in 12 states, no permit is necessary to carry a concealed handgun.

Using data from the Centers for Disease Control and Prevention’s Web-Based Injury Statistics Query and Reporting Systems database, the researchers mapped out the relationship between changes in state concealed-carry permitting laws over time and total firearm-related homicide rates between 1991 and 2015. They also examined the FBI’s Uniform Crime Reports Supplementary Homicide Reports database to differentiate between handgun and long gun homicides. Previous studies have examined only homicide by all firearms.

The researchers found that “shall issue” laws were associated with a 6.5 percent higher total homicide rate than “may issue” laws, as well as an 8.6 percent higher firearm homicide rate and a 10.6 percent higher handgun homicide rate. The researchers found no impact of shall-issue laws on long gun shootings.

The findings are particularly relevant, the researchers say, because Congress is currently considering national concealed carry reciprocity legislation, which would allow anyone to carry a gun in any state as long as they have a concealed carry permit from the state they live in. The researchers argue that adopting such a policy could lead to significant public health risks.

“The trend toward increasingly permissive concealed carry laws is inconsistent with public opinion, which tends to oppose the carrying of guns in public,” the authors write. “Our findings suggest that these laws may also be inconsistent with the promotion of public safety.”

Other SPH study authors are Ziming Xuan, an associate professor of community health sciences, Craig Ross (SPH’14), a research assistant professor of epidemiology, Sandro Galea, dean and Robert A. Knox Professor, and Bindu Kalesan, an assistant professor of community health sciences and a School of Medicine assistant professor of medicine.