Listening to commercials, one would think that chemicals are harmful and should be avoided.

Ads for carpet cleaning, household products, toiletries, pet foods and other products claim to be chemical free. The implication is that we should avoid chemicals in order to promote health and safety in the home and in the environment at large.

Exactly what are these nefarious substances known generically as "chemicals" that we should avoid?

One carpet-cleaning firm claims to use only water, no chemicals. An acne medication claims not to use chemicals but contains a list of unpronounceable substances.

What is a chemical anyway? There seems to be some ambiguity even among the arbiters of word use.

One dictionary defines it thus: "produced by or used in a reaction involving changes in atoms or molecules." Another says, "a substance with a distinct molecular composition that is produced by or used in a chemical process." Yet another: "a substance obtained by a chemical process or producing a chemical effect."

None of these tell us what a chemical is in a way that allows us to know whether a given substance is a chemical.

In fact, all matter consists of various elements and chemical compounds that are often intimately mixed together.

To put it bluntly, everything is a chemical. Claiming a product to be chemical free is actually saying it consists of nothing. Emptiness. A vacuum.

For example, water is one of the planet’s most corrosive chemicals. It is the universal solvent, capable of dissolving more other substances than any other chemical.

So what are these claims really trying to say? Do they mean no man-made chemicals, no harsh chemicals, no damaging chemicals, no unhealthy chemicals; or are they just relying on the ignorance of consumers to send a comforting message that has no basis in reality?

There also is the problem of defining a "harmful chemical," which depends on the situation at hand. Water can leave a permanent stain on a wood surface, so a product that does not contain water may be useful in polishing and preserving wood. The same product also may be poisonous and may produce permanent stains on a silk dress.

The word "chemical" needs context relating it to a particular use before its suitability can be evaluated.

Product label language that might be more useful, though also open to broad interpretation, includes "no man-made chemicals," "no harsh chemicals," "no corrosive chemicals," "no harmful chemicals" or "only safe chemicals" are used in this product.

Perhaps it is only a handful of scientists who are offended by the miscarriage of locution in claiming that anything is chemical free, but it is nonetheless incorrect and makes the companies using such marketing language guilty of either ignorance or deception.

When you hear that a product is chemical free, first of all be suspicious of the intentions, then find out what is really in the product and make an informed decision about whether the chemical ingredients are caustic, hazardous or harmless.

The one thing you know for sure is that no product is chemical free. Even the air we breathe is a chemical.

Richard Brill is a professor of science at Honolulu Community College. Email questions and comments to rickb@hcc.hawaii.edu.