Smoking heavily causes DNA mutations.

Scientists in the UK and the US have discovered that tobacco can cause hundreds of DNA mutations.

The research, published in Science, was conducted by an international team, including the Wellcome Trust Sanger Institute in Cambridgeshire (UK) and Los Alamos National Laboratory in New Mexico (USA).

Analyses have shown a direct correlation between the number of cigarettes a person smokes in their lifetime and the number of mutations in tumor DNA.

Smoking 20 cigarettes a day can cause DNA changes in many organs such as the larynx, liver, mouth, and bladder. Photo: PA.

People who smoke 20 cigarettes a day have an average of 150 mutations in each lung cell every year.

These DNA changes are permanent and persist even after a person stops smoking.

On average, smoking one pack of cigarettes a day leads to the following changes:

150 lung cells

97 cells in the larynx

23 cells in the mouth

18 cells in the bladder

6 liver cells

The study's lead author, Professor Mike Stratton of the Sanger Wellcome Trust, said: "These mutations can transform a normal cell into a cancerous cell."

Researchers say that in tissues like the lungs that are directly exposed to cigarette smoke, they can find mutagenic markers of chemicals in cigarette smoke, including at least 60 carcinogens.

However, they were unable to find a similar pattern in tissues such as the bladder when not directly exposed to tobacco smoke.

Professor Stratton says that smoking appears to be accelerating the body's natural mutation process, but how it does this remains "mysterious and complex."

Dr. David Gilligan, a consultant physician at Papworth Hospital, added: "150 mutations in cells each year correspond to 150 opportunities for lung cancer to develop."

According to Zing