Women with breast cancer are increasingly asking for removal of both breasts - despite there being no medical reason for the surgery.
Most do not have a genetic or family history putting them at higher risk of the disease, warn experts.
As a result, they are being over-treated and may suffer long-term harm, including delays in dealing with the cancer.
The rise in women asking for the procedure comes after actress Angelina Jolie last year chose a double mastectomy for prevention when she discovered gene mutations raised her risk of breast cancer to 87 per cent.
The risk is around 12.5 per cent in the general population.
But a recent study found more than two-thirds of women who had both breasts removed after a cancer diagnosis did not have a medical reason for doing so.
They had a very low risk of developing cancer in the healthy breast because they had no family history of breast or ovarian cancer, or BRCA 1 or BRCA 2 gene mutations.
The study was carried out by US researchers, but surgeons in Britain say such requests are on the increase, especially from young patients who want the unaffected breast removed at the same time.
In the US study, of 1,447 women treated for breast cancer, almost 8 per cent had undergone a double mastectomy. But 69 per cent of these women who underwent removal of the unaffected breast at the same time had no genetic or family risk factors.
Study leader Dr Sarah Hawley, from the University of Michigan, said having such a procedure "does not make sense".
"Having a non-affected breast removed will not reduce the risk of recurrence in the affected breast," she added.
"For women who do not have a strong family history or a genetic finding, we would argue it's probably not appropriate to get the unaffected breast removed."
The research, published in the journal JAMA Surgery, found 18 per cent of the women studied had considered a double mastectomy.
Women with a risky family history and BRCA mutations made up around 10 per cent of those diagnosed.
In the UK it is estimated that up to 1,200 women a year with faulty genes have preventive removal of both breasts, while the number of breast cancer patients opting for simultaneous removal of a second healthy breast is unknown.
Following Jolie's revelation last year that she had had a double mastectomy, a breast cancer charity reported a four-fold surge in women enquiring about having their breasts removed.
Figures compiled by Cancer Research UK showed the number of calls to its helpline regarding a family history of breast cancer rose in 2013 from 13 in April to 88 for May.
A total of 15,920 people went onto the pages from its website containing information about breast cancer the day of Miss Jolie's announcement, May 14. The previous day just 4,796 visited the site.
Leading breast cancer surgeon Professor Kefah Mokbel said in the past ten years there have been increasing requests for double mastectomies and reconstruction from young women diagnosed with cancer in one breast.
"They want to minimise the risk, but the study shows that women who do not have a genetic predisposition or family history are being over-treated."
Genetic testing should be used as an objective measure for women considering having a second unaffected breast removed, he said.
He warned that the procedure carries complications, such as potential psychosexual problems and possible delay in medical treatment of the affected breast, which could reduce chances of survival.
Sally Greenbrook, of Breakthrough Breast Cancer, said: "Double mastectomies are not routinely offered to women with breast cancer in the UK unless they have a family history of the disease or a high risk of recurrence as outside of these groups there is no evidence to suggest that this would be of benefit."
Baroness Delyth Morgan, chief executive of Breast Cancer Campaign, said: "Women who are concerned about getting breast cancer in their other breast should speak to their healthcare team who will be able to provide them with support and information about the risks of this occurring and their individual treatment options."
- Daily Mail