Young people would be better off travelling the world than taking part in "spurious" overseas gap-year aid projects, a volunteer charity has said.
Prince Harry spent some of his gap year volunteering in Africa
Voluntary Service Overseas (VSO) warned that "voluntourism" often cost students thousands of pounds and did nothing to help developing countries.
The gap-year industry catered for the needs of participants rather than those they claimed to help, the charity said.
Gap-year providers said good research would filter out rogue organisations.
Up to 200,000 people from the UK take time out every year according to the Year Out Group, an association of gap-year providers.
VSO said projects offered to students taking a year off were often badly planned and could have a negative impact on participants and the communities they worked with.
"While there are many good gap-year providers, we are increasingly concerned about the number of badly planned and supported schemes that are spurious - ultimately benefiting no one apart from the travel companies that organise them," said Judith Brodie, the director of VSO UK.
VSO is now drawing up a code of good practice to help young people find genuine projects abroad.
Ms Brodie added: "Young people want to make a difference, but they would be better off travelling and experiencing different cultures, rather than wasting time on projects that have no impact and can leave a big hole in their wallet."
'Outdated and colonial'
Richard Oliver, chief executive of the Year Out Group, said his organisation had been set up seven years ago to ensure gap-year providers signed up to a code of practice and provided well-structured placements.
While VSO did not deal with large numbers of young volunteers, these companies catered specifically for student needs, he said.
He added that research by young volunteers and their parents would filter out any badly-organised programmes.
QUESTIONS TO ASK PROVIDERS
What will my role be?
Who benefits from the programme?
What is the ethos of the organisation?
What will I pay for?
Is there any pre-departure training?
Does the organisation offer health and safety assistance?
Will there be someone in the country to contact?
Will I be debriefed when I get back home?
Can I speak to a previous participant?
Source: Year Out Group
"There are organisations out there that don't meet the standards we expect but it is not difficult to find them out with careful research and by asking the right questions."
These included asking who would benefit from the activities and what the ethos of the organisation was, he said.
"These providers are more often than not approached by NGOs 'in country' to ask them to get involved in projects - organisations that have something worthwhile to do," he added.
Projects Abroad, which organises gap-year programmes, said it had enabled more than 16,000 people to teach English, help out in orphanages and disability centres as well as assist with development and conservation work around the world.
Robert Kidd, the organisation's programme advisor, said: "A large proportion of our volunteers are gap-year students, and to say that this has had no impact and has been a waste of time is simply an insult to their efforts."
In June, VSO warned "consumer-driven volunteer tourism" was jeopardising the charity's development work in countries most in need.
People were increasingly approaching the organisation about volunteering "as if it was a holiday" and choosing safer destinations, the charity said.
And last year VSO said gap-year programmes risked becoming "outdated and colonial" by focusing on how UK youngsters could help poor communities, rather than what they could learn from them.