You may or may not know by reading the label.

Nearly 20% of the 84,000 chemicals being used commercially in the US—from rust removers to driveway sealants—are being legally kept secret from the public, according to the Environmental Protection Agency.

That gaping problem arose after Congress passed the Toxic Substances Control Act in 1976 to help protect trade secrets but made it rather easy for manufacturers to bypass normal regulatory scrutiny, even when it involves chemicals that could pose harm to humans.

Nearly 95% of the notices for new chemicals received by the Feds in recent years requested the silent treatment. Roughly 700 chemicals are introduced each year to the American market.

Of the nearly 17,000 secret chemicals, most are probably harmless. But chemical producers have disclosed in mandatory reports to the Feds that many pose a “substantial risk” to public health or the environment.

In March, for example, over half of the 65 “substantial risk” reports received by the EPA involved secret chemicals.

151 of the secret chemicals are made in quantities equal to or greater than 1 million tons per year. Ten of them are used in products designed for children, the EPA reports.

Select EPA employees do know the identities of the secret chemicals but they are prohibited from sharing the information with other federal or state officials, emergency responders and the public.

“Even acknowledging what chemical is used or what is made at what facility could convey important information to competitors, and they can start to put the pieces together,” Mike Walls, vice president of the American Chemistry Council told the Washington Post.

The Obama administration wants Congress to make manufacturers prove a chemical should be kept confidential, and wants to allow EPA officials to share that confidential information with state regulators who implement most EPA mandates across the country. Stay tuned.