More than 98% of supposedly natural and environmentally friendly products on US supermarket shelves are making potentially false or misleading claims, Congress has been told. And 22% of products making green claims bear an environmental badge that has no inherent meaning, said Scot Case, of the environmental consulting firm TerraChoice.

The study of nearly 4,000 consumer products found "greenwashing" in nearly every product category – from a lack of verifiable information to outright lies.

Even the experts are confused. Case, whose firm runs its own Ecologo certification programme, admitted he had bought a refrigerator only to find it failed to meet its claims of energy efficiency.

"My refrigerator used twice as much energy as advertised," he told members of the House of Representatives committee on commerce, trade and consumer protection. The hearing amounted to a crash course into the perils of the new green marketplace for the committee. Congress is looking at how to guide consumers through a thicket of competing claims on so-called greenness.

One problem is proliferation – both of products claiming to be green and of certification programmes purporting to back up those claims.

The interest in products that do not poison water or air, create unnecessary waste or unduly add to the effects of climate change has defied class divisions and the economic recession. In its company surveys, Wal-Mart, the chain of low-cost megastores, found that 57% of its customers professed to be concerned about the environment.

There is a constantly expanding pool of products to choose from. About 33% of all new food products launched in 2008 claimed to be "natural", Dara O'Rourke, a professor in environmental policy at the University of California, Berkeley, and founder of the GoodGuide, told the recent hearing. But with around 300 competing environmental certification programmes, shoppers are bombarded by irrelevant or deceptive labels touting the green, natural, eco-friendly, recyclable and non-toxic properties of goods.

It is virtually impossible to sort through the claims, said Urvashi Rangan, of the Consumers Union. "We've got to get rid of the green noise," she said. "Vague and misleading terms should not be allowed."

Labels do not generally say whether products contain recycled content, or how far they travelled from factory to shelf.

Rangan singled out "non-toxic", "natural", and "fragrance free" as misleading claims, because the federal government has never set a precise standard for manufacturers to meet. "Personal care products are the Wild West," she said.

Reading the fine print on labels will not necessarily help either. Companies are not required to disclose the use of some substances believed to be dangerous – such as phthalates, which can cause birth defects and hormone abnormalities and are widely used, from baby bottles to cleaners and cosmetics.

The makers of household cleaners are also not required by law to list every chemical in the bottle so long as it is below a certain level. "Almost none of these companies disclose the ingredients in these products," O'Rourke told Congress. "We don't know what is in them. We don't what the plastic is made of."And as Case eventually discovered, even the most seemingly reliable certifications cannot be trusted.

Case told the Congress hearing he bought his LG Electronics refrigerator in 2007, reassured by its Energy Star rating. The seal, from the department of energy, is supposed to be awarded to appliances that consume at least 20% less electricity than a standard appliance.

This spring, he got a letter saying that his fridge did not, after all, qualify for Energy Star status because LG, in its process of "self-certification", had strayed from the efficiency guidelines set by the department of energy.