Flicking through a free newspaper on the London underground recently, my attention was drawn to a half-page advert for cigarettes. I felt confused – I hadn’t seen one of these for a very long time – hadn’t they been banned? Closer inspection revealed that the ad was of course for an e-cigarette, a device that delivers liquid nicotine in vaporised form without most of the pesky carcinogens in tobacco.

The status of e-cigarettes is controversial. They are banned in Brazil and Norway but unregulated in the US and UK (although that is set to change), and there are currently few regulations on advertising them in print form in the UK. However, television and radio ads for e-cigarettes have been criticised for normalising and glamorising smoking, and for failing to mention that the products contain nicotine. Some of these ads have even been banned by the Advertising Standards Authority.

Should print adverts for e-cigarettes also be more tightly regulated? We don’t yet know whether ads for e-cigarettes appeal to smokers trying to cut down or whether they encourage young people to experiment with this safer form of nicotine delivery – early indications suggest that both forms of use are on the rise. What we do know is that, in smokers, images of real cigarettes can trigger cravings and smoking. These effects are more powerful than you might imagine. Simply viewing images of smoking and cigarettes on a PDA has been shown to trigger stronger cravings in smokers than holding an unlit cigarette.

Of course, we already know that advertising is effective, which is why ads for tobacco products have been increasingly restricted since the 1960s. The same applies to advertising of other tempting products, such as foods that are high in sugar, fat and salt. In lab studies, children and adults exposed to snack food ads during commercial breaks eat substantially more (45% more in kids) than those exposed to other ads.

Advertising works at many psychological levels – it makes products more familiar, acceptable and desirable. Images associated with a rewarding substance, such as photos of cigarettes or food, activate brain networks associated with motivation and reward. This activation varies considerably between people and can predict how much they later eat and gain weight, and how many cigarettes they later smoke.

Images like those used in ads become what psychologists call ‘conditioned stimuli’ – powerful cues that have become strongly associated with a desired substance and indicate that it is available and ready for use (think of Pavlov’s dog). These cues can trigger cravings and relapse, even after long periods of not using the substance. Some individuals are far more sensitive to the ‘triggering’ effects of cues than others. Studies in rats, for example, show that some animals are highly attracted to cues and will work almost as hard to get them (e.g. by pressing a lever) as for the drug or food itself. These cue-sensitive rats are also more vulnerable to behaviours associated with addiction and overeating.

The reason this is a problem is that, contrary to what we like to think, we actually have little control over whether we pay attention to these cues in ads. Pictures of cigarettes, food and alcohol only have to be flashed up for half a second or less to grab attention, and this effect is often linked to craving and consumption. In fact, reward-related images can even influence brain activation and behaviour when they are presented so quickly that they are not consciously perceived.

This being the case, the concern is that ads for e-cigarettes could trigger cravings in former smokers for real cigarettes. Once that desire has been activated, all one can do is try to fight it by using strategies like distraction or suppressing the urge. But instead of relying on people’s (highly fallible) self control, we could instead help prevent this craving by restricting the advertising.

Interestingly, recent ‘real world’ studies suggest that people with good self-control may resist temptation in the same way, by establishing smart habits and avoiding cues in the first place. This clearly works for some – one can choose not to have junk food at home – but it may be harder for cue-sensitive people to avoid temptation when surrounded by ads. If our self-control is even partly innate, advertising may be unfairly leading some into temptation.

Calls to restrict advertising are often met with accusations of a nanny state trying to curtail personal freedom. However when it comes to the power of advertising, we are not all equally able to resist, so tighter restrictions may in fact provide greater personal freedom to the most vulnerable among us. Perhaps it is time to have an informed public debate about advertising and offer people a say as to what images they want to be surrounded by.

When it comes to the advertising of e-cigarettes there are some reassuring noises – the Committee of Advertising Practice are developing new rules to ensure that e-cigarettes are promoted responsibly. They are planning to launch a full public consultation about this “as early as possible in the New Year”.

Natalia Lawrence is a senior lecturer in psychology and translational medicine at the University of Exeter