The Scottish government gave PWB Health a grant to develop the product
A Scottish breast cancer group has called on the retailer Boots to stop stocking a device which claims to help women detect breast abnormalities.
Dumbarton-based company PWB Health, which produces Breastlight, said it shines a light through the tissue, giving an "internal" view of breasts.
But the Scottish Breast Cancer Campaign has written to Boots to say the product could cause women "needless anxiety".
Boots and PWB Health said it should be used along with self-examination.
PWB Health was last year awarded a £165,000 grant from the Scottish government to develop the hand-held device.
Announcing the grant, Finance Secretary John Swinney described Breastlight as a "pioneering" product which had potential health benefits for millions of women.
On its website PWB said the torch-like product can be used for "earlier detection" and said it highlights any "dark clusters" which could be a cancerous lump undetectable by self-examination.
However, the Scottish Breast Cancer Campaign told Boots it was "completely unconvinced about the efficacy" of the device.
It said: "We concluded that not only was it non-user friendly but that it could cause unnecessary distress if the 'shadows' were misinterpreted by a woman, who would then have to wait for an appointment with a doctor to have her fears allayed.
"As breast cancer advocates, we pointed out to Breastlight that, even if a woman found an 'abnormality' with the light, she would find it extremely difficult for a GP to refer her on to a breast clinic on the evidence of 'shadows' produced by a torch.
"Thus the product could create needless anxiety."
The organisation said there was also a danger of women using the product instead of self-examination, and called on Boots to reconsider stocking it.
Alex Gourlay, chief executive of the retailer's health and beauty division, said: "It must be stressed that Breastlight is not a diagnostic tool and should not be used as a substitute for mammogram screening or as a replacement for general breast awareness.
"Some women may choose to use Breastlight as an accessory to their existing breast awareness practices, while others may prefer to rely on familiarity with their bodies when looking for changes to their breasts."
PWB Health also issued a statement responding to the charity's claims.
It said: "We have an ongoing dialogue with the major breast cancer charities.
"We have never sought their endorsement - they are independent bodies so it is not their policy to give it."
The manufacturers also pointed out that all its marketing material states the Breastlight is to be used along with self-examination and not as a replacement for mammography.
The spokesman added: "Breastlight has undergone extensive clinical testing to demonstrate efficacy.
"We have had no reports of increased anxiety with the product. In fact, most women feel more confident."
The company said it has sold more than 5,000 devices and claimed it had received very positive feedback from "the medical profession worldwide".