Credit: Christian Darkin/Photolibrary

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Today, cosmetic companies champion a new generation of small molecules known as peptides, which, they claim, penetrate the dermis to boost collagen and reverse deterioration by rebuilding from the inside out. The prototype is palmitoyl pentapeptide, also known as Pal-KTTKS or Matrixyl. In the test tube, these molecules do indeed stimulate fibroblasts to produce collagen. Numerous cosmetics include palmitoyl pentapetpide. Dermalogica's California-based scientific director Diana Howard hails it as the "future of skincare". Lancôme also uses a peptide derived from rice in its R.A.R.E. technology to help stop collagen bundles from disintegrating.

Another way to regenerate the dermal mattress is to re-stuff it with the sort of molecules that normally do the job: the jelly-like GAGs. While many products contain hyaluronic acid, this gigantic molecule won't penetrate the upper layers of the skin and get to where it's needed. Lancôme's Absolue range relies on a small sugar-like molecule, Pro-Xylane, that it claims is a building block for making GAGs. Lancôme's in-house literature states that it penetrates all layers of the skin and plumps the skin by increasing the amount of gelling, as well as improving the overall architecture. Still, says Finnin, "it's very difficult to assess the validity of these claims. In the scientific literature, you don't see articles about Pro-Xylane".

One way to bring senescent fibroblasts out of retirement is to restore their levels of an enzyme called telomerase. In the laboratory the results have been impressive. María Blasco, who heads the Telomerase Group at the Spanish National Cancer Research Centre in Madrid, bred a strain of genetically engineered mice whose skin cells carried extra telomerase. She found that as they aged, their skin retained a youthful ability to heal wounds. But that's not all. As she reported in the journal Science in 2005, the mice also had a greater tendency to form skin cancers.

Jerry Shay, a professor at Southwestern Medical Centre in Texas, also restored telomerase to aged human fibroblasts and showed they give rise to more youthful skin in reconstituted skin models.

One product to capitalise on telomerase research is RéVive Peau Magnifique. Its advertisement claims: "Telomerase converts resting adult stem cells to newly minted skin cells, ie recruits youth. The results are indelible and life-changing."

However, despite the rhetoric, just how cosmeceuticals activate the telomerase enzyme in the fibroblasts of the dermis is far from clear. "I am very sceptical about cosmetics that claim to rejuvenate skin via telomerase activation," says Shay.

At a meeting of American dermatologists in 1991, cosmetic dermatologic surgeon Alastair Carruthers astonished his colleagues by announcing that in the future they would soon be using one of the most deadly known toxins for the treatment of wrinkles. He was right. Frowning and smiling eventually etches deep furrows into overlying skin; skilfully injected Botox (a toxin made from the bacteria that causes botulism) smooths out wrinkles by paralysing discrete muscle groups.

Cosmeceutical companies are not taking this lying down, however, and are mounting a challenge using peptides that mimic the paralysing effects of Botox. Argireline and Myoxinol, found in Payot's Rides Relax Regard, for instance, are claimed to have this effect. Studies show that in the test tube, these agents can interfere with the signals that trigger muscle contraction. But how they work when applied to intact skin is another issue. The chemicals would have to traverse not just the epidermis, but the dermis then the fatty hypoderm layer beneath to reach the muscles beneath. Even other cosmetic companies find this preposterous. Says Dermalogica's Howard: "the claims for Botox alternatives are all bogus". Lancôme's Delvigne adds, "It's wrong to claim an effect on the nerve endings and muscles; these are under the hypoderm, they are very, very deep."

THERE'S NO DOUBT the active ingredients of some cosmeceuticals have effects on cells in test tubes or mice. You can trawl through volumes of this research in journals such as the International Journal of Cosmetic Science or Dermatologic Surgery, much of it carried out by the cosmetic giants L'Oréal, Unilever, and Proctor & Gamble. But the big question for consumers is: do the skincare products we buy off the shelf have the same effects on human skin?

"The short answer is there isn't any evidence", says Stephen Shumack, the Honorary Secretary of the Australasian College of Dermatologists. Shumack doubts that today's cosmeceuticals do anything different from yesterday's cosmetics. "Personally I would recommend people save their money for a nice holiday and use vaseline and sunscreen," says Shumack. Choice magazine, published by the Australian Consumers' Association, supports Shumack's view. In June 2007 it published a 12-week road test of 11 cosmeceuticals. "Any improvements were considered only 'slight' and there was no relationship between the type of active ingredient and overall performance, nor did price relate to performance," the report said.

Barrie Finnin agrees it's unlikely that the active ingredients in most cosmeceuticals can penetrate skin. It takes small molecules with exceptional water and oil solubility characteristics to breach this layer. When it comes to something like palmitoyl pentapeptide, which would need to wend its way through multiple cell layers all the way down to the dermis to stimulate collagen synthesis, Finnin says, "I'd be surprised if it does penetrate." Even with his study on Myoxinol, during which Finnin used special techniques to coax the chemical into the skin of volunteers, he has no idea why it produced results. He says the effects were too fast to be explained by new collagen synthesis.

All of this is highly frustrating for Finnin, whose research over the years has focussed on developing techniques to deliver drugs to the skin and verify that they are effective. But few companies are jumping at the chance to prove that their products really work. "My only explanation is that they're afraid the authorities will jump on it," says Finnin.

So it's not just consumers being left in the dark. Not even scientists know what these products actually do. The cosmeceutical industry operates outside of accepted scientific methodology. The in-house studies of cosmetic companies have to be taken with a grain of salt, and the scientific literature that does exist doesn't seem to address the fundamental questions: do the active ingredients penetrate human skin? Do they do it in the mixtures found in creams? What concentrations do they reach? What effects do they have when they get there?

At best, cosmeceuticals do no harm, apart from relieving beauty seekers of surplus income. At worst, if they are truly active, then their safety and long-term effects remain quite unknown. "If you feel muddled by this, you're getting the right picture," says Finnin. "None of this is black and white."

As for whether they're 21st century snake oil, there's no question the products are peddled by a mammoth marketing machine: one that is exceptionally adroit at exploiting our insecurities and skilled at making authentic and scientific sounding claims while skirting the regulatory authorities. Should we continue to indulge in treating ourselves to anti-ageing elixirs and their like? If they make us look a little better and feel a little more confident, then they could well be worth the expense. Just take their scientific claims with a pinch of NaCl.

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