You are sitting in a freshly drywalled house, drinking coffee from a Styrofoam cup and talking on a cellphone. Which of these is most likely to be a cancer risk?

It might be the sitting, especially if you do that a lot.

Despite all the recent news about possible cancer risks from cellphones, coffee, styrene and formaldehyde in building materials, most of us probably face little if any danger from these things with ordinary use, health experts say. Inactivity and obesity may pose a greater cancer risk than chemicals for some people.

“We are being bombarded’’ with messages about the dangers posed by common things in our lives, yet most exposures “are not at a level that are going to cause cancer,” said Dr. Len Lichtenfeld, the American Cancer Society’s deputy chief medical officer.

Linda Birnbaum agrees. She is a toxicologist who heads the government agency that just declared styrene, an ingredient in fiberglass boats and Styrofoam, a likely cancer risk.

“Let me put your mind at ease right away about Styrofoam,” she said. Levels of styrene that leach from food containers “are hundreds if not thousands of times lower than have occurred in the occupational setting,” where the chemical in vapor form poses a possible risk to workers. “In finished products, certainly styrene is not an issue,” and exposure to it from riding in a boat “is infinitesimal,” she said.

Carcinogens are things that can cause cancer, but that label does not mean that they will or that they pose a risk to anyone exposed to them in any amount at any time.

They have been in the news because two groups that periodically convene scientists to decide whether something is a carcinogen issued new reports.

Last month, the International Agency for Research on Cancer, part of the World Health Organization, said there is a possibility cellphones raise the risk of brain tumors.

“The operative word is `possibility,’” said Lichtenfeld, who among others has pointed out the thin evidence for this and the fact that cancer rates have not risen since cellphones came out.

Last week, the National Toxicology Program, part of the National Institute of Environmental Health Sciences, both of which Birnbaum heads, issued its report.

It adds to the list of known carcinogens formaldehyde, which is in building materials and some hair-straightening products, though Birnbaum said on-the-job exposure is the main worry. The list also adds a plant substance in some ”natural” arthritis remedies, aristolochic acid. Six other things were called “reasonably anticipated” to be carcinogens, including styrene and another herbal medicine ingredient, riddelliine.

Since 1971, the international cancer agency has evaluated more than 900 substances. Just over 100 have been deemed carcinogens, 59 are called probable carcinogens, and 266 are possible ones.

In this last category of possibles, besides the electromagnetic energy from cellphones, are coffee, engine exhaust and talc-based body powder. Talc in its natural form may contain asbestos, although products sold for home use since the 1970s have been asbestos-free. Again, most risk is thought to involve occupational or unusual exposure to natural talc.

The evidence on coffee has gone back and forth for years, with no clear sign of danger and some suggestions of benefit.

However, known carcinogens include alcoholic beverages, estrogen treatments for menopause symptoms, birth control pills, certain viruses and parasites, and even some drugs used to treat cancer, such as cyclophosphamide and tamoxifen.

“Most people would probably be shocked to see the number of things they interact with every day’’ on these lists, Lichtenfeld said.

Here is the problem: The agencies that pass judgment on a carcinogen do not regulate it or determine what levels or routes of exposure are a concern and for whom. 

(AP)