They've been around for decades and are found in everything from candy to yogourt to salad dressing. Now, the Food and Drug Administration in the U.S. is examining whether artificial food dyes are hazardous and cause hyperactivity in children.

The FDA has long said that no studies have shown a definitive link between food colourings and behavior or health problems in children.

But on Wednesday and Thursday, the agency will ask a panel of experts to review the latest evidence and advise on whether it should study the issue further, or call for policy changes which could include warning labels on food.

The panel could also recommend Thursday that the FDA do nothing at all.

The meeting is in response to a 2008 petition filed by the influential advocacy group Center for Science in the Public Interest, which wants the FDA to ban eight artificial food dyes. The group is particularly concerned with Red No. 40, Yellow No. 5 and Yellow No. 6, which make up 90 per cent of the food dyes on the market.

In background documents released ahead of the two days of meetings, FDA staff scientists write that while most children might be unaffected by food dyes, there are concerns that "certain susceptible children" with behavioral disorders might have their conditions "exacerbated by exposure to a number of substances in food, including, but not limited to, synthetic color additives."

For the general population, however, the FDA "concludes that a causal relationship" between the dyes and hyperactivity "has not been established."

The CSPI worries that the effects of food colours may be cumulative, noting that per capita consumption of food dyes in the U.S. has increased five-fold since 1955. Many of the foods containing the dyes are directly marketed to children, such as breakfast cereals and fruit snacks.

The CSPI's director Michael Jacobson concedes that completely banning the dyes would be difficult, but is hoping the FDA will at least put warnings on food package labels.

The American Council on Science and Health, a science watchdog group that often does battle with the CSPI over its claims, says the fears about food colours are overblown.

It says that even if a small subset of kids were sensitive to food dyes, banning all of them would be like banning penicillin for everyone in order to protect the one per cent orf so of the population allergic to the antibiotic.

The Grocery Manufacturers Association also insists food colours are safe.

"All of the major safety bodies globally have reviewed the available science and have determined that there is no demonstrable link between artificial food colors and hyperactivity among children," the group said in a statement.