Mothballs, air fresheners and cancer

What do mothballs and some air fresheners have in common? They both contain chemical compounds which are carcinogenic.  Mothballs and some air fresheners contain the chemicals paradichlorobenzene (PCDB) and naphthalene. A recent study from the University of Colorado has pinpointed why these chemicals can cause cancer. Both chemicals have been found to block apoptosis, the normal process of “cell suicide”.

“Apoptosis serves as a checking mechanism to ensure that the right amount of cells are generated in the body,” said Dr. Ding Xue who headed the research team. In Alzheimer’s disease and Parkinsons’s disease, too much apoptosis is occurring, while in cancer and autoimmune disorders, too little apoptosis occurs, he explained. The study showed that both chemicals blocked enzymes which initiated apoptosis.


More than 1 million pounds of naphthalene and PDCB are used by consumers annually. The chemicals are most commonly found in solid toilet block deodorizers, solid and spray air fresheners, and moth balls and crystals. One company describes its product this way,

            Closet Freshener block is made of pure Paradichlorobenzene crystals and top quality fragrance pressed into large 275 gram rectangles with a hanger built right in. When the cellophane wrapper is slit or removed, the "para-zene" begins to evaporate, releasing a clean fresh scent. Our assorted pack contains Lavender, Summer Potpourri, Pine, and Cedar.

Parachlorodibenzene is a pesticide. The US EPA requires that moth repellent products containing  paradichlorobenzene bear warnings such as "avoid breathing vapors"  to warn users of potential short-term toxic effects.  Yet paradichlorobenzene is also the key active ingredient in many air fresheners.  Paradichlorobenzene is also an eye irritant and, according to the US National Toxicology Program, possibly causes reproductive damage.

The Janitor’s Product Pollution Prevention Project places PCBD in the category “Do Not Use - Severe Health Risk to Janitor and Building Occupants.”

Naphthalene and PDCB have been shown to cause cancer in rodents and are classified by the National Toxicology Program and the International Association for Research on Carcinogens as potential human carcinogens. However,  their biochemistry has not been well understood, said Xue.

The methodology used in the study may mark a  scientific breakthrough in determining whether other chemicals may cause cancer in humans. " For the first time, we have developed a systematic way to screen virtually any potential cancer-causing chemical that may affect humans using these nematodes as animal models, " said Hue. The study was published in the June 2006 issue of Nature Chemical Biology.