There's no such thing as a healthy smoking habit--and if you think a quick puff every now and then won't hurt you, it's time to get your head out of those tobacco clouds.

A new study finds that even limited smoke exposure can be harmful--causing the genetic changes that can lead to serious and even deadly long-term health problems.

And that means trouble, not just for "social smokers," but for anyone who has to venture through clouds of secondhand smoke.

Researchers measured nicotine levels in 121 people, and then divided them into three groups: nonsmokers, low- exposure smokers, or active smokers. Then, they took cell samples from the airways--sensitive areas most affected by smoking and exposure to tobacco.

Using those samples, the researchers scanned each person's entire genome. Essentially, that means they were able to see how the genes changed as a result of smoke exposure.

They found that there are about 370 genes that react to the smoke, and those reactions are the cellular equivalent of panic and chaos: genetic changes and abnormalities at nearly any level of exposure.

The researchers said these genetic changes are like the proverbial "canary in a coal mine," a warning from the body that something very wrong is taking place.

"The canary is chirping for low-level exposure patients, and screaming for active smokers," Dr. Ronald Crystal, senior author of the study, said in a news release.

He didn't mention that the canary eventually drops dead, but that's what's coming--because it doesn't take a new study like this one to find drawbacks to smoking.

In addition to the risk of cancer, emphysema, and heart disease, smoking has been linked to everything from depression to impotence. One recent study even found that smokers are less intelligent than nonsmokers.

There's a reason even the most hardcore smokers are usually trying to quit. But the new study shows you don't have to be a pack-a-day puffer to face those risks--they can also come from a supposedly moderate tobacco habit, whether it's the so-called social smoking or even just an occasional butt with a coworker as an excuse to get out of the office for 10 minutes.

And if the new study is accurate, you might even want to hold your breath if you have to walk past those smoking colleagues crowded around building entrances.