Smoking leaves an "archaeological record" of the hundreds of DNA mutations it causes, scientists have discovered.

科学家研究发现，吸烟会导致DNA突变，给人留下数百种基因突变的“永久记录”。

Having sequenced thousands of tumour genomes, they found a 20-a-day smoker would rack up an average of 150 mutations in every lung cell each year.

The changes are permanent, and persist even if someone gives up smoking.

Researchers say analysing tumour DNA may help explain the underlying causes of other cancers.

The study, in the journal Science, was carried out by an international group, including the Wellcome Trust Sanger Institute in Cambridgeshire and the Los Alamos National Laboratory in New Mexico.

The analysis shows a direct link between the number of cigarettes smoked in a lifetime and the number of mutations in tumour DNA.

The authors found that, on average, smoking a packet of cigarettes a day led to:

150 mutations in each lung cell every year

97 in the larynx or voice box

23 in the mouth

18 in the bladder

six in the liver

Joint lead author Prof Sir Mike Stratton, from the Wellcome Trust Sanger Institute, said: "The more mutations there are, the higher the chance that these will occur in the key genes that we call cancer genes, which convert a normal cell into a cancer cell."