Children and teenagers are being bombarded with videos and pictures of unhealthy food online, polling suggests.
The poll added that youngsters more likely to engage with content about junk food if it is shared by influencers.
Cancer Research UK said that ministers must do more to protect young people from “harmful marketing that could increase their risk of obesity and cancer in the future”.
New laws, which come into force next year, will end paid-for advertising, including online, of specific foods which are high in fat, sugar and salt.
The charity said that it is important for the implementation of the legislation to go ahead as planned after repeated delays.
And it warned that not all exposure to junk food will end when the new laws come into place as there will still be online advertising loopholes.
The charity surveyed 4,000 children and young people aged 11 to 21 across the UK and found:
- Half (52 per cent) saw unhealthy food and drink products from either businesses or influencers on social media in the last month.
- Almost four in 10 (39 per cent) said they engaged with these posts by commenting, liking or sharing.
- They were more likely to interact with a post from an influencer compared to a business.
Some reported that seeing content about food high in fat, salt and sugar made them feel tempted or hungry.
“A giant cookie bowl keeps showing up, when I see it, I feel like ordering a dessert and I feel really hungry,” an 11 year-old told the charity.
A 15-year-old said: “I’d say at least every two minutes that I’m on Instagram I’d see at least one food-related post.”
Liv Cheek, prevention policy manager at Cancer Research UK, said: “Being overweight or obese is the second biggest cause of cancer in the UK after smoking, and rates among young people are rising.
“Our survey shows more than half of young people regularly see unhealthy food and drink content online, often promoted by influencers.
“Advertising can shape what children eat, so the UK government must help create an online environment that empowers, rather than undermines, healthy changes.
“Planned restrictions on junk food advertising online are a vital step to protect young people’s health.
“However, these measures must be properly enforced and strengthened by closing any remaining gaps in the online marketing rules.
“We urge the UK government and regulators to take bold action to shield young people from harmful marketing that could increase their risk of obesity and cancer in the future.”
Next month, experts will meet at the The International Food Addiction and Comorbidities Conference in London to discuss growing health concerns about food addiction.
The Daily Express reported organisers believe that some 10 million people in the UK are hooked on junk food including pizza, chocolate, crisps, biscuits and ice cream.
The Department of Health and Social Care has been approached for comment.
