Encouraged by an email exchange with Stan, I spent the last few days researching silicones. They crop up in many shampoos, conditioners and moisturizers (as well as breast implants), with aliases such as dimethicone, hydroxypropyldimethicone or amodimethicone. The claims made about silicones are starkly black or white: they are good for you or they are very bad for you. Since both statements are unlikely to be simultaneously true, some Truth In Aging perspective is needed.

Before we go into what is true or false, it is worth knowing that silicone is either an organic or inorganic polymer. And a polymer is made up of many molecules strung together. Depending on the structure of how these molecules link up, polymers could be soft and bouncy, rock hard or gooey and gel-like. Hence, different silicones can play different roles in cosmetics.

Silicones build up on the hair causing it to be dull and heavy - true or false?

This depends on the silicone. Cyclopentasiloxane (CPS), for example, is water-thin so it’s very good at dispersing thicker, greasier silicones. For this reason it’s often used in combination with dimethicone. It is also volatile, which means it will evaporate. So, not only does it help spread heavier silicones, but it doesn’t leave your hair feeling weighed down after it’s done.

Silicones will make your hair fall out - true or false?

The theory is that silicone in shampoos and conditioners builds up on the hair and deprives the shaft of oxygen with the result that hair falls out. This appears to be untrue. The Journal of Investigative Dermatology says: "Silicone-based conditioners, such as dimethicone, are one of the newest agents that aid in smoothing the cuticle and increasing hair smoothness and luster. The silicone is left behind following water rinsing of the shampoo as a thin coating over each individual hair shaft to fill in visible defects in the hair cuticle. Probably the most important aspect of hair cosmesis is combing ease. Increased hair friction snags the hair as the comb is drawn for grooming purposes, resulting in hair breakage. This is the most common cause of significant hair loss in normal patients, patients with dandruff, and patients afflicted with female pattern hair loss. Compatibility of the hair can be increased by smoothing the cuticle and coating each individual hair shaft with an agent to decrease friction. Silicone fulfills this need."

Some people are allergic to silicone - true or false?

I've seen quite a few people remark on online message boards that they are allergic to 'cones. This is mostly likely to be false and they are allergic to some other ingredient (perhaps a preservative). Unlike many preservatives that are known irritants, countless tests have been conducted with silicones that have concluded that they do not cause allergic reactions. Having said that, unmodified silicones stay on or near the surface of the skin. Not only are the molecules too big to physically enter past the upper living cells, they associate with the upper layer of drying skin but they also cannot penetrate cell membranes due to their large size. In some ways that is a good thing, however, they may be preventing stuff - sweat - from getting out. There have been some recent studies that show that prolonged exposure of the skin to sweat that can't escape causes irritation.

Silicones can cause cancer - true or false?

This question came to head when women with silicone breast implants made an association with leakage of the gel and subsequent development of cancer cells. This is where things really get black and white. The evidence for whites (silicone does not cause cancer) looks to be compelling. Until, that is, you come to the realization that the evidence is based on research carried out decades ago. The most quoted is the most problematic. It was conducted by Dow Chemical (maker of silicone) on one group of rats, just after the Second World War.

I also came across a reference to a review of 123 reports on cyclic polydimethlsiloxanes (D3, D4, D5, and D6). The review concluded: "These compounds are volatile and potentially of concern in manufacturing; however, they also are used in consumer products, such as hair sprays, and are found in breast implants, although in very low amounts (see Chapter 3). They are practically nontoxic on ingestion, dermal application, or inhalation, although they are mildly irritating when placed directly on the skin or in the eyes. Subacute gavage studies showed that these compounds had no untoward effect other than a reversible increase in liver weight due to increases in both cell number and cell size at doses ranging up to 2,000 mg/kg. Skin application did not cause toxicity; however, some D5 penetrates the skin."

I was about to breath a sigh of relief until I discovered that the  reports were all 40 years old.

And then I found this: according to research gathered by attorney Richard Alexander, of the Alexander
Law Firm in San Jose, California, Dow Chemical and Dow Corning have been aware of the toxic effects of silicone and silica since the 1950s, based on their own studies, but never published the data. They knew these substances were bioreactive, immunogenic, toxic, and inflammatory when introduced into the human body, states Alexander. (Update on Breast Implants, January 1998, website: http://consumerlawpage.com.)

"Silicone degrades into silica, usually at the surface of the gel implant, then fragments and subdivides into millions of microdroplets capable of migrating throughout the body" (according to PSC Records No. 1352, 7017. These are documents produced by Dow Corning in national litigation. Silica in the body is a toxic, carcinogenic substance, damaging the immune system, killing cells, and producing silicosis.

Silicone is toxic - true or false?

True, I'm afraid. The Journal of Toxicology reported that silicone injections led to multi-organ failure. Research collected by the Plaintiff's Steering Committee (PSC) for the National Breast Implant Litigation shows that silicone has marked effects on the adrenal glands and liver, induces chronic inflammation, and degrades into smaller molecules, including silica. Silicone fed to rabbits produced widespread toxic effects including kidney and spleen damage within four months. (Stanford Medical Bulletin, 10:1 [1952], 23-26.) "That silicone is toxic in both animals and man is well proven," stated John S. Sergent, M.D., and colleagues in Textbook of Rheumatology (W.B. Saunders Company, 1993).

OK, but I am not injecting or ingesting silicones and I have the breasts that God gave me, so I am not in any real danger - true or false?

This is a bit trickier and enters a realm dappled with shades of grey. If the silicone molecules are too large to enter the surface of the skin and, as is the case with cyclopentasiloxane (in vitro tests show that less than 2% penetrates the skin), it evaporates quickly, then there probably isn't too much to fear from your shampoo or moisturizer. On the other hand, silicones can help some ingredients penetrate the skin more effectively. Dow Corning sites some research with silicone and hydroquinone in which "the silicone gum induced the formation of a reservoir of hydrocortisone in the stratum corneum".

In the same paper, Dow Corning becomes at best ambiguous about the safety of topical silicones. It cites tests on rats that led to enlarged livers and testicular cancer. But then says, without any back-up, "this effect is not applicable to humans" —provided that the silicone "was allowed to evaporate."

But silicones have some benefit or there wouldn't be so much of it in my bathroom - true or false?

Largely false. Even those that are described as "skin conditioning" or "conditioning agents" are entirely superficial and temporary, imparting a silky, feel-good factor, but without actually doing anything at the cellular level. There is an argument that silicones protect you from other nasties, such as polluted air. Hmm, but at what cost?

Silicones that you can expect to see in cosmetics and hair care:

Dimethicone (also called Polydimethylsiloxane), Methicone, Amino Bispropyl Dimethicone, Aminopropyl Dimethicone, Amodimethicone, Amodimethicone Hydroxystearate, Behenoxy Dimethicone, C30-45 Alkyl Dimethicone, C24-28 Alkyl Dimethicone, C30-45 Alkyl Methicone, Cetearyl Methicone, Cetyl Dimethicone, Dimethoxysilyl Ethylenediaminopropyl Dimethicone, Hexyl Methicone, Hydroxypropyldimethicone, Stearamidopropyl Dimethicone, Stearoxy Dimethicone, Stearyl Methicone, Stearyl Dimethicone and Vinyl