Women posting bare-faced selfies online have helped a leading cancer charity raise more than £8m in six days – despite thousands of pounds being donated to Unicef by mistake.

The craze has seen soaring numbers of women posting pictures of themselves wearing no makeup on social media sites and nominating their friends to do the same.

Cancer Research UK, which did not start the campaign, said the #nomakeupselfie trend had resulted in an unprecedented increase in donations.

But it has emerged that some people intending to donate to the charity sent their cash to Unicef in error, while others mistakenly inquired about adopting a polar bear with the World Wildlife Fund (WWF).

Cancer Research UK and Unicef use the same text number for donations but those texting the keyword DONATE rather than BEAT found their money sent to the UN agency.

Mike Flynn, director of individual giving at Unicef UK, said there had been a "genuine mixup" and it was working with Cancer Research UK to transfer £18,625 that was donated by mistake.

He said: "Unicef UK is not responsible for this error. However, we have been working hard to find a resolution to the situation for those affected.

"We contacted Cancer Research UK as soon as we became aware of what was happening. Unicef UK and Cancer Research UK have agreed that these donations will be received in full by Cancer Research UK.

"We are now working closely with all parties involved to ensure that this doesn't happen again in the future."

The WWF confirmed that it too had accidentally received text messages. Those texting BEAR instead of BEAT accidentally inquired about adopting a polar bear through the charity. The WWF said no money had been taken from people who sent the texts.

Kerry Blackstock, the charity's director of fundraising, said: "Any texts sent to us instead of Cancer Research would not result in any donations going to help protect polar bears as WWF relies on human operators calling people back to confirm adoptions, so no money would have changed hands.

"When we realised there was a lot of interest in a campaign we weren't presently running we made sure our automatic text message response let the sender know their text had gone awry.

"We wish Cancer Research every success in their campaign and their goals. Polar bear selfies are harder to come by, though as far as we are aware none wear makeup."

Carolan Davidge, Cancer Research UK's director of communications, said: "We're really grateful to everyone who donated to Cancer Research UK through the #nomakeupselfie campaign.

"We have agreed with Unicef that the donations they received will be given to Cancer Research UK. People who made a donation in error to Unicef have already been contacted to let them know the money is being transferred."

A host of famous women including the pop stars Beyoncé and Rihanna, model Cara Delevingne and X Factor judge Cheryl Cole have taken part in the trend, which has spread across Facebook, Instagram and Twitter.

Cancer Research UK said the donations would allow the charity to carry out 10 clinical trials that it did not have money to fully fund last week.

Harpal Kumar, chief executive of Cancer Research UK, said: "We have been overwhelmed by the support people have been showing us through the #nomakeupselfie trend.

"We don't receive any government funding for our research and so it is phenomenal to think that the generosity of the public is enabling us to fund critical research that we didn't have the money for six days ago. Being able to fund more trials will bring forward the day when all cancers are cured.

"It has been an exciting week, and we would just like to thank everyone again for their support."