In every breath, myriad chemical clues to illness

Scientists have long known that when you get sick, it can sometimes show in your breath -- if only you know what to look for. But only recently have they had the tools to detect trace chemicals produced by cells whose chemistry is going awry.

That discovery is feeding the next generation of breath tests.

Crucial to the test is not the shallow breath from the upper part of our lungs but the breath derived from alveoli, the tiny chambers at the tips of the bronchial air passages, deep inside. Alveoli are lined with membranes loaded with tiny blood vessels. The chemicals in the blood easily cross this membrane so that the alveolar breath “mirrors the composition of the blood,” says Dr. Michael Phillips, inventor of one of these breath tests and an internist at the New York Medical College in Valhalla.

In one test under development, a combination of nine different volatile organic chemicals, including a principal one named nonane, and others known as octanes and propanes, have been found to be present in the breath of women who have breast cancer.

A combination of volatile chemicals, including ones named alkanes, are diagnostic of early lung cancer.

In both cases, the tests don’t rely upon chemicals that are unique to these diseases, but rather to combinations of chemicals.

Although these new tests go further than ever before, smelling the breath to diagnose illness is not a new idea. Doctors dating back to Hippocrates have paid attention to patients’ breath.

Breath that smells of ammonia warns of kidney failure. A sweet sickly smell reminiscent of rotting apples can indicate uncontrolled diabetes: It’s caused by the chemical acetone.

(Plain old stinky breath means our teeth may be rotten.)

In 1971, Nobel Laureate Linus Pauling ushered in the modern era of breath analysis when his research revealed that human breath contained more than 200 different organic compounds.

Because the technology wasn’t yet available, he couldn’t identify those chemical constituents with any degree of certainty.

Since then, armed with modern analytical equipment, scientists have identified hundreds of breath compounds. They also discovered that illnesses such as cancer, diabetes and heart disease trigger the excess production of volatile chemicals that leave their fingerprints in the air we exhale.