Stress has an impact on the way we live, work and interact with others and, it turns out, the environment can stress out our cells, too, a new study suggests.

Environmental factors such as pollution, bacterial toxins and tobacco smoke can turn on genes in cells that are supposed to be off, said researchers from the Biotech Research and Innovation Centre at the University of Copenhagen in Denmark.

When cells are exposed to damaging outside factors, they may have to change to survive. Genes activated by stressors from the environment have the potential to disrupt normal fetal development and cell function, the researchers said.

For example, stress can cause brain cells to produce hormones and other chemical signals they're not supposed to produce, disturbing normal brain function, according to the study.

The study adds to mounting evidence showing how stress can affect the body on a cellular level, said Alice Liu, a cell biology professor at Rutgers State University of New Jersey, who was not affiliated with the study.

Stress has always been known to affect the body in large-scale and microscopic ways whether through increased production of stress hormones in the body or by changes in gene expression, Liu said.

The new study found the environment influences genes by affecting the proteins called histones. In cells, histones act like spools around which the thread of DNA is wound. This helps organize longs strands of DNA within the cell.

When everything is going smoothly, other signals inside cells tell histones which genes should be off and which should be on.

But when a cell is exposed to environmental stress factors, those signals get messed up. They bind to the histones and turn the genes on that should be off, according to the study.

But because it's impossible to avoid environmental stressors, people should try to limit their physical and mental exposure so stress-induced genes can return to their normal states as soon as possible, said Beverly Emerson, a professor at the Salk Institute for Biological Studies in California, who was not involved with the study.

Fortunately, humans' genetic programming is flexible and genes can return to normal when stress signals go away, Emerson said, but "it is important to avoid prolonged stress, which may lock genes into a permanent 'on' state."

The study was published today (Sept. 24) in the journal Molecular Cell.