Cervical cancer experts warned young women today against buying DIY smear tests over the internet.
Dr Anne Szarewski, a clinical consultant at the Wolfson Institute of Preventive Medicine in London, spoke out as online pharmacy DrThom launched the kits.
She said they could lead to women under 30 being told they have the sexually-transmitted infection that causes cervical cancer when it would actually clear up on its own.
The new test detects changes in genetic material in cells affected by human papillomavirus (HPV), which causes most cases of cervical cancer.
The £115 service is being aimed at busy career women, those who find going for smear tests embarrassing or younger people who fall outside the current age group for screening on the NHS.
Women in Scotland, Wales and Northern Ireland receive NHS screening from the age of 20 but those in England are only eligible from the age of 25.
Screening ages were the subject of debate after TV star Jade Goody died last year from cervical cancer aged 27.
Dr Szarewski said: "In young people, everyone is going to test positive. The rate of HPV is high but it's transient...it comes and goes."
She said women whose results suggested something was wrong could be left feeling anxious.
"Women will be paranoid and they will not be eligible for an NHS colonoscopy.
"So, they are going to be paying a few hundred pounds more for a colonoscopy privately, which is unnecessary.
"For women under 30 I don't think there's a call for HPV testing. It's going to create a lot of worry among women."
Professor Peter Sasieni, a Cancer Research UK epidemiologist, said while the charity supported making smear tests more accessible, it could not support the DrThom test "because there is a lack of published data on how effective this would be.
"Also HPV infection in young women is extremely common and mostly harmless.
"It is not clear what proportion of women under 25 would test positive but it could exceed 15%.
"In these cases it is not clear what back-up would be provided, who would pay if DrThom recommended colposcopy (an examination by a gynaecologist) or whether GPs would know enough about the test to counsel patients.
"Given that the DrThom test will miss a proportion of women with disease who would be identified had they gone to their GP for screening, what advice would be given to women who test negative?"
The one-hour test being sold by DrThom can be carried out in a woman's own home, with results usually coming back within three weeks.
It involves inserting a special tampon and wearing it for one hour to enable a "smear" of cells from the cervix to be obtained.
The test is then placed inside a secure envelope and posted to the DrThom laboratory.
Results are uploaded to a secure online patient record - created by the woman when she registers for the service - on the DrThom website.
Following the results, a woman can ask doctors for advice and guidance online or, for an extra £15, can have a telephone consultation with a GP.
According to DrThom, the test is less likely than a traditional smear test to give a 'false positive' result.
This is when a test indicates something is wrong when it is not - in this case falsely suggesting a woman has changes to her cells that need investigating.
Nick Wales, consultant gynaecologist at the Chelsea and Westminster Hospital NHS Foundation Trust in London, and one of the medical team overseeing the test service, said: "It is an invaluable addition to the detection of pre-cancerous changes of the cervix.
"We have successfully used it in those women unable to tolerate a vaginal examination.
"I believe within 10 years all cervical screening will be done this way."
Dr Thomas Van Every, medical director of the DrThom website, said: "While the scientific community works hard to improve the detection capability of the traditional smear, many women are too busy or anxious about having a smear to take part in the NHS Screening Programme in the first place.
"We hope this test will offer an alternative as well as being another avenue to help women understand the risk of cervical cancer, the importance of being screened and the availability of vaccination against it."
The launch comes after a study out last week showed home smear tests could detect many more cases of cervical cancer.
Published in the British Medical Journal (BMJ), research found self-test kits for HPV could double the number of women diagnosed.
More than 2,800 women a year in the UK are diagnosed with cervical cancer and almost 1,000 die from it every year.
Another 24,000 women get smear test results each year showing severely abnormal changes to the cells of their cervix, indicating the likelihood of cancer unless treatment is given.