WASHINGTON (AP) ― Tobacco companies will be required to report the levels of dangerous chemicals found in cigarettes, chew and other products under the latest rules designed to tighten regulation of the tobacco industry.

The preliminary guidance issued Friday by the Food and Drug Administration marks the first time tobacco makers would be required to report quantities of 20 chemicals associated with cancer, lung disease and other health problems. The FDA will release the information in a consumer-friendly format by next April.

“Cigarettes are the only mass-consumed product in this country for which consumers don’t know what’s in them, until now,” said Dr. Lawrence Deyton, director of FDA’s tobacco center, in an interview with the Associated Press.

Ammonia, carbon monoxide and formaldehyde are among the ingredients or byproducts of tobacco that are subject to the new rule.

Regulators have identified more than 93 harmful or potentially harmful chemicals in tobacco products, though the agency is only focusing on 20 for the coming year. The agency will take comments on the guidance until June 4. There is no deadline for when the documents will become final.

A law enacted in 2009 gave the FDA authority to regulate a number of aspects of tobacco marketing and manufacturing, though the agency cannot ban nicotine. FDA also gained authority to set standards on levels of harmful ingredients in tobacco products, though the agency is not yet using that power.

The same law lets the agency approve new tobacco products that could be marketed as safer than what’s currently for sale.

In separate guidance issued Friday, the FDA laid out the scientific studies it will require before any company can market a so-called modified-risk tobacco product. Companies must submit extensive testing data on health risks for users and non-users, behavior changes and consumer understanding of marketing materials for new products.

“The law sets a high standard to make sure that tobacco products marketed to reduce risk actually reduce risk,” Deyton said.

The FDA’s handling of modified-risk products has been highly anticipated by both the public health community and bigger tobacco companies, which are looking for new products to sell as they face declining cigarette demand due to tax increases, health concerns, smoking bans and social stigma.

Some tobacco companies have alternatives like snus - small pouches like tea bags that users stick between the cheek and gum ― and dissolving tobacco ― finely milled tobacco shaped into orbs, sticks and strips. But they are not explicitly marketed as less risky than cigarettes.

The FDA is required to respond to a company’s application within a year of its submission and acceptance. FDA officials would not comment on how many applications have been submitted to date.