Smokers leave a chemical marker of their addiction in their DNA, a new study finds. These markers could help measure smokers’ risk of cancer, according to Medical News Today.

Researchers found sites in the DNA of blood that were chemically tagged as a result of smoking. The tags can be detected in lung tissue, and could be used to measure increased risk of cancers of the lung, breast and bowel, they said.

These tags, or modifications, are found on the surface of DNA, and do not change the underlying genetic code, the researchers explained. The tags gradually diminish once a person stops smoking, according to lead researcher James Flanagan of Imperial College London. A former smoker’s DNA will never exactly match the unmarked DNA of a person who never smoked, he noted.

In a news release, Dr. Flanagan said, “Using this approach, we will be able to read the fingerprint on a person’s DNA to tell us a story of how their habit may have changed over the course of their life.”

The findings were presented at the NCRI Cancer Conference this week.