According to the the British Association of Aesthetic Plastic Surgeons (BAAPS), BII is a term used by patients who have breast implants and describes a variety of generalised symptoms that they feel are directly connected to silicone implants.
Symptoms can include tiredness, “brain fog”, joint aches, immune-related symptoms and sleep disturbance, the organisation explains.
However, BII is currently not recognised as a medical diagnosis and therefore there are no diagnostic criteria nor investigative protocols to treat is as such.
That said, medical experts are now calling for more research into the illness and for women to be told about the condition prior to undergoing breast implant surgery.
Naveen Cavale, the UK's National Secretary for the International Society of Plastic Surgery, told the BBC’s Victoria Derbyshire programme: "As far as some of my patients are concerned, breast implant illness is a very real thing for them, and I have no reason to doubt them. But, to me, as a doctor, it makes no scientific sense.
"Breast implant illness isn't something we used to always talk about - but the proper plastic surgery associations such as ourselves, have started advising we do so, which I think is a good thing for patients to make more informed decisions."
Nora Nugent, consultant plastic surgeon of BAAPS, added: "Surgeons should be warning patients about breast implant illness. Patients need the most up-to-date information possible, with the caveat that breast implant illness is poorly understood. So it's going to be difficult to give absolute information."
The Medicines and Healthcare products Regulatory Agency (MHRA) states it received 1,586 Adverse Incident Reports for breast implants between 2014 and May 2019.
While the regulator states that there is no new evidence of an increased risk to patients, last month it said it was willing to reconsider its position on breast implant illness after medical concerns were highlighted by the Channel 4 documentary series Dispatches.
“Patient safety is our highest priority and we always investigate where there are safety concerns raised about a medical device,” a spokesperson said at the time.
“It’s entirely reasonable that book should be opened again now, and we and our advisory group are already looking at the evidence around this. We would be eager to learn more from patients about their experiences in this area.”
BAAPS agrees with the MHRA's guidance on breast implants, telling patients that “there is no need to remove or exchange any current implants based on the most up-to-date scientific data available”.
During the programme, Naomi Macarthur, a 28-year-old fitness instructor, explained that she received breast implants in 2014 but within weeks of the incident she revealed she began to suffer “the most horrific symptoms”.
"I remember getting severe pain in my stomach," she told the programme. "And the tiredness was like I had run a marathon and dug a million trenches and I hadn't done anything. Writing with a pen was too tiring."
Macarthur suffered several symptoms including hair loss, allergies and rashes.
Despite being told her condition was unrelated to the implants by medical professionals, Macarthur sought support from women on online groups who had suffered similar symptoms that they believe resulted from their breast implants.
Last year, Macarthur had her implants removed and said that she soon found her symptoms to disappear.
“I can’t believe how much I’ve bounced back,” she added.
BAAPS states that on average, around 50 per cent of women who self-identify as having BII feel that their symptoms improved after implant removal – sometimes temporarily and sometimes permanently.
Steph Harris, from Woking, concurred with Macarthur, revealing she has had three different types of implants and has experienced symptoms of breast implant illness.
“Dealing with the breast cancer was easier,” Harris told the programme. “That’s going to sound really strange. Chemotherapy was much easier to deal with than the chronic fatigue…I’ve been through both and this is harder.”
In 2010, PIP breast implants were withdrawn from the UK after it was found they had been fraudulently manufactured with unapproved silicone gel, and were far more prone to splitting (rupturing) than other breast implants, the NHS explains.
It is estimated around 47,000 British women had PIP implants fitted prior to the withdrawal, most of whom are still living with them.
In 2016, the NHS set up the Breast and Cosmetic Implant Registry which details all breast implant procedures completed in England and Scotland by both the NHS and private providers.
In April, France's National Agency for Medicines and Health Products (ANSM) ruled that the macro-textured and polyurethane breast implants for cosmetic and reconstructive surgery would be banned due to a slight risk of patients developing a rare form of non-Hodgkin lymphoma.
However, the MHRA said the implants would continue to be sold in the UK.
“Based on our analysis of the latest scientific evidence and expert clinical advice our advice remains the same," a spokesperson said.
"There is no new evidence of an increased risk to patients and there is no need for people with breast implants to have them removed.”
Read more about breast implant safety here.
The Independent has contacted the MHRA for further comment.