Check any package of bacon, hotdogs, or cold cuts and chances are you'll find nitrites listed among the ingredients.

Although nitrites have caused cancer in laboratory animals and may well do the same in people they are among the oldest and most common food preservatives and serve a variety of functions.

What Are Nitrites?

Nitrites and their close relatives, nitrates are simple compounds made of oxygen and nitrogen attached to some other element such as sodium or potassium. Potassium nitrate, or saltpeter, as it was called, was first used in the middle ages.

Today, sodium nitrite is the most common food preservative.

Red Meat

Fresh meat in the supermarket is red because of the pigment called "myoglobin," which stores oxygen in muscle cells. But myoglobin is only red when it is bonded to oxygen molecules.

In live animals, the blood carries oxygen to the myoglobin; in freshly cut meat the oxygen comes directly from the air. But the red color of freshly cut meat is temporary since aging, cooking, and bacteria, all separate the oxygen from the myoglobin, turning the meat a brownish-gray color.

What Nitrites Do

Nitrites keep meat red by bonding to the myoglobin and acting as a substitute for the oxygen. Oxygen and sodium nitrate both turn myoglobin red, but nitrate attaches with a more stable bond and so the color lasts longer.

Although for several hundred years, nitrites and nitrates have been used to preserve the color of meat, more recent evidence shows that these chemicals also inhibit the growth of bacteria, including the bacteria that cause the deadly disease, botulism.