Cigarettes leave you with more than a smoky scent on your clothes and fingernails. A new study has found strong evidence that tobacco use can chemically modify and affect the activity of genes known to increase the risk of developing cancer. The finding may give researchers a new tool to assess cancer risk among people who smoke.

DNA isn’t destiny. Chemical compounds that affect the functioning of genes can bind to our genetic material, turning certain genes on or off. These so-called epigenetic modifications can influence a variety of traits, such as obesity and sexual preference. Scientists have even identified specific epigenetic patterns on the genes of people who smoke. None of the modified genes has a direct link to cancer, however, making it unclear whether these chemical alterations increase the risk of developing the disease.