Vaping could trigger widespread genetic changes linked to cancer and chronic disease, scientists have warned.

A study has found regular e-cigarette users show altered activity in more than 3,000 genes, including many associated with cancer, heart disease and lung conditions.

Researchers say some of these changes may be driven not just by how much someone vapes, but what e-cigarettes they use, with certain flavours and types linked to far greater disruption.

The findings add to growing evidence that the devices, often marketed as a way to quit smoking, carry their own health risks.

However, experts stress the study was small and does not prove vaping causes disease, instead highlighting early biological changes that could signal potential harm over time.

Because vaping is relatively new, its full long-term health impact remains unclear. But scientists say heating e-liquids produces chemicals that may affect gene expression and could impair the body's ability to repair damage.

In the latest study, published in Frontiers in Oncology, researchers compared gene activity in 83 people, including vapers, smokers and non-users.

They found that those who vaped had 'altered expression' in 3,124 genes - meaning these genes were functioning in a potentially damaging way - compared with people who neither smoked nor vaped.

Almost two-thirds of these changes were linked to the type of vape flavour and device used, rather than simply how often someone vaped.

Fruit flavours, and mixing multiple flavours, were associated with the greatest changes in gene activity, while more advanced refillable devices, known as 'mods', also showed stronger effects.

Fruit flavours were linked to changes in 31 per cent of affected genes, while using multiple flavours was linked to changes in 64.3 per cent. 

Sweet flavours affected 2.9 per cent and mint or menthol 0.9 per cent.

Senior author Professor Ahmad Besaratinia, from the University of Southern California, said: 'One major question has been what's driving these biological changes.

'Is it vaping itself, or the way people vape, including the products they use?

'Our findings suggest flavourings and device characteristics play a crucial role.'

Researchers analysed cells taken from inside participants' cheeks, using RNA sequencing to track changes across thousands of genes.

They also found vapers showed more variable patterns of gene activity than smokers, suggesting potentially unpredictable biological effects.

Further analysis linked these genetic changes to a range of disease-related pathways. 

Cancer showed the strongest association, followed by endocrine, digestive and neurological conditions.

Professor Besaratinia added: 'Each flavour contains different chemicals that can produce distinct biological effects.

'This is something regulators need to consider carefully when assessing the safety of e-cigarettes.'

The findings come as regulators face mounting pressure to clamp down on youth vaping and flavoured products. 

In the UK, the Government has already moved to ban disposable vapes due to fears they are fuelling a surge in teenage use.

While experts agree vaping is less harmful than smoking, largely because it does not produce tar or carbon monoxide, it is not risk-free. 

E-cigarettes still contain low levels of potentially toxic substances, including formaldehyde, which can trigger inflammation and cellular changes linked to disease.

Smoking remains the biggest killer, with lung cancer claiming more than 33,000 lives a year in the UK. It is also the leading cause of COPD, which affects around 1.7 million people and kills 30,000 annually.

But scientists warn vaping could still contribute to the long-term disease burden. Rates of head and neck cancers, including those affecting the mouth and throat, have risen by more than a third in Britain since the early 1990s, particularly among younger adults.

While smoking, alcohol and HPV remain the main drivers, experts say vaping may emerge as a contributing factor.

Researchers are now working to identify which chemicals in vaping liquids are responsible for the genetic changes. 

Professor Besaratinia said: 'If we can pinpoint these compounds, regulators could require manufacturers to reduce or eliminate them, helping minimise potential harm.'