It used to be that a boob job meant a pneumatic change in silhouette. But times have changed, and so have the women who want bigger breasts. Rather than being young and “out there” they are older, in their late thirties to mid-forties and they want something a little more discreet. They don't want the boobs of a pop star, they just want the breasts of their youth.

Hence the rise and rise of the latest cosmetic enhancement the“boob jab”, an injection that promises a subtly enhanced bust which should last for 18 months, without the trauma of surgery. It's been available for a year and already 2,000 women have had their breasts increased by it.

As a beauty journalist I was offered Macrolane injections - or the “boob jab” - to write about but I didn't read the small print. If I had, I might have realised that there was less research behind it than I'd imagined. I didn't read the consent form which said that its use “for breast enhancement has not been established” and that in small studies adverse reactions had included “development of hardness of the breast, formation of palpable lumps and capsular contraction”, I might have saved myself lumpy and uneven breasts.

Macrolane, an injectible gel made from naturally degradable hyaluronic acid, came on the market with a wave of excited publicity last year. Its appeal is that it provides instant results before the substance disintegrates and is expelled by the body. Private clinics are pushing it hard.

I was an ideal candidate - my small bust had shrunk to nothing after three children. As a beauty writer, I was keen to try it for professional as well as personal reasons - not least because the product comes from Q-Med, a Swedish biotech company with an exemplary record in producing safe, well-tested hyaluronic acid-based wrinkle-fillers such as Restylane. So I signed the form in a rush. Before I underwent the procedure the surgeon told me about the potential risks and in half an hour it was all done. Even with only 100ml of gel injected in each breast, I was suddenly shapely, almost a proper A-cup, and I was thrilled.

That was last March, and I went on being thrilled all summer until, by August, one breast had mysteriously gone rock hard while the other had shrunk to half its size. On holiday I resorted to padding out my sundress with a sock, to even them up. In September I went back for a top-up. My surgeon, Chris Inglefield at London Bridge Plastic Surgery, reckoned that the right breast had “encapsulated”, meaning the tissue around the injected gel had decided it was a foreign substance and started to harden up to fence it off, which used to be a regular problem with old-style breast implants; I hadn't realised that it could happen.

Mr Inglefield broke up the encapsulation with firm massage, and gave me a top-up of Macrolane so that both sides were even. Again, I was delighted - though had I been a normal paying customer, I might have been less than delighted to be forking out [see prices, right]. But a few weeks later I found a lump, down to the side of the right breast. I shot back to see Mr Inglefield, who reassured me that it was nothing sinister, just a portion of the gel that had moved to one side and hardened. Firm massage should soften it up. It did. But by then I finally started asking questions.

Was it normal to have all these incidents in the space of eight months? I went back, belatedly, to the consent form. Right near the top was a surprise. “The use of Macrolane™ VRF20 and Macrolane™ VRF30 for breast enhancement has not been established,” it said.

Asking around among cosmetic doctors, surgeons and cosmetic spa-managers, I heard that my experiences - particularly in regard to the loss of volume - were not uncommon while David Ross, consultant plastic, aesthetic and reconstructive surgeon who is head of plastic surgery at Guy's and St Thomas' hospital and practises privately at The London Clinic, is one who would not dream of using Macrolane. “I have significant reservations about injecting artificial materials into the substance of the breast,” he says. “While many of the hyaluronic-acid-based materials have been shown to be safe when used around the face and in small volumes, we have to be much more cautious when injecting material in and around the breast. We have to be certain it doesn't interfere with breast screening. Several years down the line, will there be changes, even benign changes? If there is infection or bleeding around the Macrolane, that will cause scarring in the tissue, which again may affect the interpretation of mammography. ”

I went to Q-Med's official Macrolane website, which states carefully that Macrolane is a type of non-animal hyaluronic acid that has been “clinically proven and well documented in facial aesthetics for over 10 years with Restylane”. But have they been proven on the breast? That's where things begin to get hazy.

Q-Med puts a lot of weight on a Japanese study published in the Japanese Journal of Plastic and Reconstructive Surgery in 2006, which found that out of 1,100 people treated for NASHA breast augmentation, there were no long-lasting side-effects and breasts remained “soft and natural” for up to 12 months. Q-Med acknowledges that “longer term follow up would be desirable”. None of this means that anything illegal is happening. Regulation of substances injected into the body for cosmetic purposes is loose in the UK. Macrolane for breasts was approved in the EU on the basis of a study into its use for correcting liposuction deformities, and a currently unfinished study on its use on breasts in 24 people. Neither examined long-term effects, so people who are using it now are guinea pigs.

This is very different from the United States, where injectibles have to go through the Food and Drug Administration's rigorous approvals procedures. Macrolane is not yet approved, and may not be for a while: Q-Med's Restylane was launched in 1996 but only received FDA clearance in December 2003.

The Q-Med press office told me: “Macrolane was in development for more than seven years and underwent extensive preclinical testing and scrutiny before being approved. It will not compromise the clinical conditions or the safety of patients.”

Friends are horrified when I relate all the above. I'm none the worse for it, the only additional markings are two tiny injection scars just below my bra-line, and I have no complaints about the excellent surgeon who treated me. But I do feel the product under-delivers and does not seem to be backed up by the sort of studies that we might expect.

Additional research by Simon Crompton

Need to know

In its first year 2,000 women have used Macrolane, compared with 8,449 women who have had surgical breast augmentations, a procedure that has been available since the 1960s.

Macrolane costs up to £3,000 for a treatment that should last 18 months with £1,000 for a boost, although prices are dropping. This compares with £5,000 for a surgical breast enhancement, which should last ten years.

A study of Macrolane in 100 patients is nearing completion in Japan, while another study of 75 patients is under way in Sweden and France. A British trial is still awaiting approval.

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