More than eight in 10 adults are unlikely to become foster carers, a charity said, warning of a fostering crisis.
Over 85% of UK adults surveyed on behalf of Action for Children showed little or no interest in fostering, the charity found.
Some 4,262 adults in England, Northern Ireland, Scotland and Wales were surveyed by YouGov in July 2017.
The charity said the shortage was hitting teenagers with complex needs the hardest.
It has been exacerbated by demographic shifts which mean more foster carers over 50 are retiring.
Action for Children director John Egan said: "These shocking figures reveal the true scale of the current fostering crisis in the UK.
"Across the country, we have more and more children and young people who desperately need the stability a foster carer can give them yet we have fewer and fewer foster parents.
"We think the lack of interest, in fostering teens in particular, is down to fear of the unknown as well as a shift towards a less altruistic society in general."
The charity is running a virtual reality campaign in September to encourage more people into foster caring.