The warning labels are shocking, and they are meant to be.

Photos of cancerous growths, surgical holes in throats, amputations, gangrenous feet, and dying people are shown on cigarette packages from 120 countries and mandated by their governments to stand out.

But in the United States, where the Centers for Disease Control and Prevention reports that more than 480,000 people die each year as a result of smoking and more than 16 million Americans are living with a smoking-related illness, there are small, text-only warnings on cigarette packages.

University of Pennsylvania researchers at the Annenberg School for Communication analyzed more than 300 photo warning labels to see what was most effective in getting smokers to quit. They found that images of diseased body parts and those that showed impacts on real people were the most influential.

Cigarette package warnings from India and Thailand.
Canadian Cancer Society
Cigarette package warnings from India and Thailand.

The study was published last week in the medical journal Tobacco Control.

"Humans act in response to our emotions," said Jazmyne Sutton, lead author. "When we feel a negative emotion — fear, disgust, etc. — we want to avoid the source of that emotion."

Researchers noted that in 2009, Congress instructed the U.S. Food and Drug Administration to require the use of pictorial warning labels. The mandate was held up by legal challenges from tobacco manufacturers and a retailer. In September, a court order was issued stating that the FDA must speed up its timeline.

The researchers showed 1,400 smokers recruited for the study images on cigarette packs from Australia, Canada, New Zealand, and the United Kingdom, as well as pictorial warnings proposed by the FDA that have not yet been implemented, anti-smoking messages produced by the tobacco companies, testimonial pictorial warnings developed for an experimental study, and ads used in various local and national campaigns.

They hoped to home in on some of the features — such as image color, use of male or female characters, and presence of medical equipment on the packs — that might improve or impede an ad campaign's effectiveness and help guide future designs, said Joseph N. Cappella, senior author.

Last month, the Canadian Cancer Society published a similar report ranking countries on the size of their warning labels on cigarette packs. The U.S. was last out of 206 countries.

Timor-Leste, Nepal, and Vanuatu were the top three.

Large graphic photos on cigarette packages are a cost-effective way to get a public-health message on the dangers and consequences of smoking across not only to users but to family, friends and co-workers who also see the images, Canadian researchers found.

The most effective warnings were those that covered more than 50 percent of the packaging, they found.