Thermography machines are not approved to test for signs of breast cancer in Canada, contrary to claims being made by some medical clinics, according to federal health officials.

Health Canada issued a public advisory on Wednesday, a day after a CBC News investigation found medical authorities were questioning claims that thermography can detect signs of breast cancer earlier than mammography and other tests.

"No thermography [thermal imaging] machines have been approved to screen for breast cancer in Canada," the advisory from Health Canada states in part.

Thermography uses a heat-sensitive infrared camera to take images of the body. Proponents claim it can detect cancerous tumours in breast tissue years earlier than mammography. (CBC)

"Health Canada is not aware of any clinical evidence that thermography can be used effectively as a screening technique for the early detection of breast cancer," it adds.

"As such, it may present a potential risk to women relying on the results."

The CBC News investigation identified dozens of medical clinics across Canada that offer thermography for breast examinations.

Proponents of the technology claim while thermography is not a substitute for other tests, it can detect cancerous tumours and other signs of breast cancer years earlier than mammography.

Thermography uses a heat-sensitive infrared camera to take images of the body. The images are assessed elsewhere, often in the U.S., before the results come back.

However, the Canadian Cancer Society and medical experts worldwide say there is no proof that thermography actually works as a diagnostic tool for cancer.

They say false positives from thermography tests are gumming up the system, resulting in patients worrying about the results of tests that have no value.

Alternatively, the tests may be giving others a false sense of security about their health, they warned.

Border alert issued

The U.S. Food and Drug Administration has sent warning letters to those making assertions about thermography's benefits in that country.

But before the CBC News investigation aired on Tuesday, no such action had been taken in Canada.

Health ministers in Manitoba and Newfoundland and Labrador have since issued cease and desist orders against medical clinics in those provinces that offer and promote the benefits of thermography in detecting breast cancer.

And on Wednesday, Quebec's College of Physicians announced it will launch an investigation into thermography's claims.

"The thermography question is under investigation, because what we are worried about is that it's an illegal practice of medicine," said Dr. Charles Bernard, the college's general director.

Health Canada officials have also issued a border alert, stopping unlicensed thermography devices from being imported into the country.

The federal department says it's following up with manufacturers of thermography devices to make sure "they are aware that it is illegal to advertise or sell these types of machines to screen for breast cancer in Canada."

Health Canada is advising patients that thermography machines "are not a replacement for routine monitoring and screening for breast cancer."