COSMETIC SILICONE SAFETY

This is the second of a two-part article on silicones in hair care and pet care.  The articles were originally published in the eGroomer Journal in 2013.  

SILICONES: THE QUEST FOR TRUTH

PART TWO - SAFETY OF COSMETIC SILICONES

In Part One of the quest for truth regarding silicone ingredients, several types of silicones were identified and discussed the properties of various cosmetic silicones and some of the myths surrounding this class of ingredients.^{(1 )}It became obvious that the number of silicone ingredients is huge.  Cosmetic silicones outnumber many other categories of ingredients.  In the EU Cosmetics Directive Ingredient Inventory, for example, a search under “Dimethicone” will bring up 414 ingredients. ⁽²⁾ That is quite a family, much more than groomers usually expect.  And the 414 are only ingredients with “dimethicone” in the name.  There are many more.

Myths abound in the fertile fields of the Internet.  In Part One, we addressed myths about the properties and functioning of cosmetic silicones.  For example, a common misstatement is that silicones don’t allow the skin to breathe, while the truth is that a primary feature of these ingredients is that they form a permeable layer that seals in moisture but allows the skin to breathe. ⁽¹⁾ In Part Two, we will cover the safety assessment of the various types of cosmetic silicones that might be utilized in pet grooming products.  The official US, EU and Canada databases will be reviewed. 

There are little to no regulations regarding the safety of ingredients used in pet products.  In the US, the FDA has broad regulatory authority over human cosmetics, but nothing set up to regulate animal grooming products.⁽³⁾  The same holds true for Canada and the EU^{(4) (5)}.  Fortunately, most of the ingredients, and all of the silicone ingredients used in grooming products have been evaluated for safety in human cosmetics. 

CANADA – Canada law requires that “no person shall sell a cosmetic product that has in it any substance that may injure the health of the user when the cosmetic is used according to its customary method.”⁽⁶⁾

  Guidelines for meeting this requirement are laid out in the Cosmetic Ingredient Hotlist – List of Prohibited and Restricted Cosmetic Ingredients. ⁽⁷⁾ If an ingredient is not found on the Hotlist, it is regarded as safe. The list is updated often through the Healthy Environments and Consumer Safety Branch (HECSB) of Health Canada.  Compliance is monitored and enforced by Regional Product Safety Inspectors.

EUROPEAN UNION - The European Union requires that cosmetic products placed on the EU market be safe; that is, they “must not cause damage to human health when applied under normal or reasonably foreseeable conditions of use.”

As in the U.S., manufacturers are responsible for ensuring that cosmetic products comply with the law before they are marketed. The manufacturer or importer of cosmetics is responsible for demonstrating that the product is safe for its intended use. ⁽⁸⁾ The EU Cosmetics Directive includes annexes that are lists of substances that must not be used (Annex II), and those that have restrictions or specifications of use (Annex III). The EU also has lists of approved ingredients for all colorants, preservatives, and ultraviolet filters that are allowed in cosmetics under specific conditions. ⁽⁹⁾ To be included on an approved list, an ingredient first must be evaluated scientifically for its level of risk. The Scientific Committee for Consumer Products (SCCS) conducts safety assessments by a review of all pertinent research on an ingredient and issues an opinion. The SCCS is the scientific advisory body to the European Commission and no substance can be regulated without its opinion.  A good example of the SCCS safety review and opinion on ingredients is the opinion on Cyclomethicone (D4 & D5). ⁽¹⁰⁾

UNITED STATES - The US Food & Drug Administration (FDA) has broad authority under the Federal Food Drug and Cosmetics Act (FD&C Act and the Fair Packaging and Labeling Act.  The sale of an unsafe or “adulterated” cosmetic is prohibited. Unlike the EU, which has the most rigorous regulations, US cosmetic companies are not required to register their cosmetic establishments, file data on ingredients, or report cosmetic-related injuries to FDA. However, companies are encouraged to register their establishments and file Cosmetic Product Ingredient Statements with FDA's Voluntary Cosmetic Registration Program (VCRP). Cosmetic products and ingredients are not subject to FDA premarket approval authority, with the exception of color additives. However, FDA may pursue enforcement action against violative products, or against firms or individuals who violate the law. ⁽¹¹⁾

 Safety Assessment is done by an board of experts, the Cosmetics Ingredient Review Expert Panel (CIR).   The CIR is funded through the cosmetics industry, specifically the Personal Care Products Council but operates independent of the FDA and the PCPC.  The CIR operates from a strict set of procedures that are very transparent, with mostly open meeting and publication of the minutes of Board meetings.  The CIR reviews all published research on an ingredient (or set of similar ingredients), and allows industry experts and knowledgeable stakeholders to present additional data and information to fill in any data gaps.  ⁽¹²⁾

The Panel may make one of four basic decisions regarding an ingredient:

            Safe ingredients — Ingredients safe in the practices of use (product categories) and concentrations of use for each product category as documented in the safety assessment. ⁽¹³⁾

            Unsafe ingredients — These are ingredients with specific adverse effects that make them unsuitable for use in cosmetics.

            Safe ingredients, with qualifications — The Panel may reach the conclusion that an ingredient can be used safely, but only under certain conditions. Qualifications frequently relate to maximum concentration, but may also address rinse-off versus leave-on uses and other restrictions. ⁽¹⁴⁾

Ingredients for which the data are insufficient — If the Panel reaches an “insufficient data” conclusion, it does not state whether the ingredient is safe or unsafe. The Panel is, however, describing a situation in which the available data do not support safety. The specific data that would allow the Panel to complete its assessment always are identified.

Using the databases available for Canada, European Union and United States, the status of silicone ingredients is summarized in Table One.

CLICK HERE TO VIEW TABLE.

Are Silicones Harmful to the Environment?

         Many websites make a big to-do about silicones not being biodegradable.  The definition of biodegradable is the capability of being decomposed by bacteria or other living organisms. It is true that silicone fluids are not biodegradable.  However, the linear siloxanes, PDMS, do degrade in the environment into silicates, carbon dioxide, and water.  In water treatment, they settle into the sludge, where they are harmless to soil, water, or living organisms. ^(16)(17) The relationship of dimethicone and other PDMS linear siloxanes to the environment has been thoroughly studied and they are not considered hazardous or potentially hazardous to the environment. They do not bioaccumulate, i.e., they do not build up in the bodies of living organisms, because their molecular size is too large to pass through cell membranes.  Furthermore, tests on organisms that dwell in aquatic, soil or sediment have shown no adverse effects at concentrations well above those found in the environment. ⁽¹⁸⁾

            The environmental fate of the cyclic siloxanes (Cyclomethicone D4 & D5) is not so unambiguous. Great confusion ensued 2008 when Health Canada identified the cyclomethicones D4 (octamethylcyclomethicone) and D5 (Decamethylcyclopentasiloxane) as possibly warranting environmental measures (having potential for human and environmental harm). This concern was the result of the discovery of some detectable levels of D5 discovered in biota tissues at an arctic environmental monitoring site.  Based on a statistical model, it was concluded that D4 & D5 cyclomethicones might bioaccumulate in the Canadian environment in significant amounts.   In 2009, Canada added D4 & D5 List of Toxic Substances.  The silicone industry jumped to the defense and conducted further study and review of existing data.  The statistical model that had predicted a potential problem was discredited and flaws in the antartica sampling were identified.  The Canadian Environmental Minister appointed an independent expert panel to review the environmental data pertaining to D5. In 2012, the findings of the panel were endorsed by the Canadian Environmental Minister and D5 was cleared.  D4 was not granted a review, and industrial use of D4 is monitored and restricted.  Cosmetic uses of D4, however, have been given a "safe as currently used" pass. ⁽¹⁹⁾ (CES Cyclosiloxanes - Env. Data)(sehsc) Unfortunately, few of the cosmetic policemen websites have been updated with the current status of cyclomethicone. 

It could be said that, when it comes to the Internet, any bad news regarding silicones is persistent and accumulative, and is rarely upgraded to reflect the current science.

Do Silicones Cause Cancer?

            Dimethicone Copolyols are a group of silicone ingredients that have been made water soluble through a process of ethoxylation involving ethylene oxide.  The manufacturing process results in a toxic by-product, 1,4 Dioxane, which has been classified as "likely to be carcinogenic to humans" by the EPA. The FDA notes that:

They can be identified by having "PEG," "Polyethylene," "Polyethylene glycol," "Polyoxyethylene," "-eth-," or "-oxynol-. in their ingredient names.  The amount of Dioxane that ends up in an ethoxylated ingredient can be minimized by a process of vacuum stripping at the time of manufacture.  The principle of toxicology that"the dose makes the poison" applies here.  The FDA states that: "…the levels in cosmetic products are far lower than those found to be harmful in feeding studies and, for the most part, the types of products in which it is found are only in contact with the skin for a short time." ⁽²⁰⁾ Dimethicone Copolyols, all of which are PEG copolymers, have been thoroughly reviewed by the CIR Expert Panel and reported to be safe as currently used in cosmetic products. ⁽²¹⁾ Because studies in the 1970's showed a connection between Dioxane and cancer in animals fed high levels of the substance, any mention of PEGs conjures up a cancer fear and is exaggerated and exploited for purposes of negative marketing. 

Cancer scares work so well that this one has been generalized from the silicone polyol (PEG) ingredients and applied to all cosmetic silicones by many sensationalist writers.

Do silicones cause tumors? 

         The only studies that showed formation of tumors involved injection of silicone compounds.  There were no tumors associated with oral, dermal or inhalation routes.  To state or imply that cosmetic silicones may be linked to tumors is simply irresponsible. 

Are Silicones Endocrine Disruptors?

            Another of the accusations hurled by those that hate silicones is that they are endocrine disrupters and are potentially toxic to reproduction.  It is true that the European Union SCCS reviewed a study that indicated that the cyclic siloxane D4 (cyclomethicone) produced an estrogenic effect.  D4 was subsequently classified as Reprotoxic Category III.  A substance in this category is allowed to be used in cosmetics as long as it does not exceed the No Observable Adverse Effect Level (NOAEL).  The truth is that D4 is mostly used as an intermediary in the manufacture of other silicone ingredients and is usually present in a product in only trace amounts.  It is found as a part of the cyclomethicone mixture of D4/D5 in varying amounts.  D4 is largely an environmental concern.

We found a recent study that measured the estrogenic effect of D4 on two strains of rats compared to the effects of synthetic estrogen and phytoestrogen (plant based). A linear siloxane (HDMS) was also tested for comparison to the cyclic D4.

            Partial Results: D4 showed weak estrogenic and antiestrogenic activity.  D4 was approximately 585,000 times less potent than synthetic estrogen in Sprague-Dawley  (SD rats) and 3.8 million times less potent than synthetic estrogen in Fisher 344 (F-344) rats.  D4 was about 46 times less potent than the phytoestrogen coumestrol in SD rats. Coumestrol is an isoflavonoid found in many soy products, which has been shown to have weak estrogenic activity. The linear siloxane, HDMS, was also tested and showed no estrogenic or antiestrogenic activity. ⁽²²⁾

The design and protocols in this study were scientifically complex, sophisticated and rigorous.  The study measured and compared several dimensions and endpoints, including the effects on the two different strains of rats.  The differences in study results between these two rat strains have made comparison of some studies quite challenging. 

            Although the findings are quite lengthy, there are two things we can take away from this study: Linear siloxanes, such as dimethicone and amodimethicone, are not reprotoxic; while the cyclic siloxane D4 can have a mild estrogenic effect, this effect is quite minimal and 46 times less potent than a naturally occurring plant phytoestrogen.

CONCLUSION: The above study illustrates well how toxicology science is advancing and evolving a body of knowledge about the effects of cosmetic ingredients, while the Internet bloggers and websites keep recycling fearful misinformation.  All of the references for this paper were found on the Internet.  Accurate information is available for those who search for the truth.  The truth about cosmetic silicone ingredients is, with the exception of some of the newest entries on the playing field, silicones have been rigorously reviewed and tested.

The latest research supports the conclusion that the silicone ingredients we have looked at are safe for humans, the pets in our care, and the environment.