Your chronological age is often quite different from your biological — or “molecular” — age, which is defined by your cells’ physical condition. Everyone ages at different rates, depending on how well they take care of themselves, and whether they’re exposed to factors like stress, tobacco, and even environmental toxins.

These external factors that have an effect on your body’s biological age are called gerontogens. In a new study out of the University of North Carolina, and published in the journal Trends in Molecular Medicine, scientists found that exposure to environmental gerontogens — toxic things like benzene, cigarette smoke, and stress — can have a significant impact on your aging process.

“The rate of physiologic, or molecular, aging differs between individuals in part because of exposure to ‘gerontogens,’ i.e., environmental factors that affect aging,” Norman Sharpless, an author of the study and a member of the UNC Lineberger Comprehensive Cancer Center, said in a press release. “We believe just as an understanding of carcinogens has informed cancer biology, so will an understanding of gerontogens benefit the study of aging. By identifying and avoiding gerontogens, we will be able to influence aging and life expectancy at a public health level.”

One of the biggest environmental toxins is cigarette smoke, Sharpless notes, which even if inhaled as secondhand has been associated with lung diseases and cancer, pulmonary fibrosis, and atherosclerosis. Then there’s UV radiation from the sun, as well as chemotherapy treatment, which can speed up aging; pollutants from industrial emissions; and of course, lifestyle factors like eating too much, living sedentarily, and undergoing damaging stress.

“Mammalian aging is complex and incompletely understood,” the authors write in the article summary. “Although significant effort has been spent addressing the genetics or, more recently, the pharmacology of aging, the toxicology of aging has been relatively understudied.”

For quite some time, researchers have attempted to create a testing system, or biomarker, that could measure your molecular age. Different ways to do this could involve measuring the beta-amyloid in the brain, though this wouldn’t necessarily reflect aging in other areas of the body. Scientists could also measure telomere length — these are the little caps at the end of our DNA strands that slowly wear down over time. Research has shown that exercise can actually lengthen our telomeres, presumably expanding our life span — and that stress can shorten them. There’s also the process of senescence, which refers to aging in the sense of cells that stop dividing.

In 2009, Sharpless and his team discovered how to use a blood test to identify the levels of a certain protein called p16INK4a, which is often increasingly found in mammalian organs the older they get, and in senescent cells (which increase as we get older). Levels of this protein are also associated with physical inactivity and smoking. They considered this blood test a “major step toward a practical tool to clinically determine a person’s actual molecular age, as opposed to just their chronological age,” Sharpless said in 2009. But he also notes that just one biomarker isn’t going to do the trick. “You need a panel,” he told National Geographic. “The perfect test doesn’t exist, but I’m certain that within my lifetime we’ll have the ability to measure someone’s physiological age with precision.”

Indeed, it’s often shocking to see the difference between an 80-year-old who is bedridden and an 80-year-old who is running marathons. Perhaps the entire point of Sharpless’s research is to better understand how aging isn’t necessarily just a matter of genetics; but about exposure to environmental factors as well, so scientists can find ways to prevent premature aging. “The idea that environmental factors can accelerate aging has been around for a while, [but] I agree that the study of gerontogens has lagged behind other areas of aging research,” Judith Campisi of the Buck Institute for Research on Aging told National Geographic.

Sharpless plans to continue research in this area to help push it forward. “We believe the comparison of molecular markers of aging to clinical outcomes should begin in earnest,” Sharpless said.

Source: Sorrentino J, Sanoff H, Sharpless N. Defining the toxicology of aging. Trends in Molecular Medicine. 2014.