BAKERSFIELD, Calif. -- Smokers know that cigarettes are bad for their health, but the habit may be even more toxic than they realized.

New research has found that smokers can inhale enough secondhand smoke that it is like consuming several extra cigarettes per day.

Doctors from the National Cancer Research Institute in Italy studied smokers who worked in newsstands -- enclosed areas that could be especially dangerous due to reduced air circulation. They used air samplers to measure each worker's external exposure to tobacco smoke.

Results showed that the accumulation of secondhand smoke was adding an extra 2.6 cigarettes each day.

Researchers said most studies haven't even considered the possibility that passive smoking could be an added health risk for smokers, when in truth, they are the ones who spend the most time breathing it in -- further increasing their odds of cancer and heart disease.

It's yet more reason to quit, experts said -- but at a minimum, smokers should refrain from lighting up in tight spaces such as cars or poorly ventilated rooms at home.