And most importantly: Is it safe?
What is Silicone?
The plastics industry considers silicone a plastic, regardless of much of the green marketing claiming it is not a plastic.
Technically, silicone could be considered part of the rubber family. But, if you define plastics widely, silicone is something of a hybrid between a synthetic rubber and a synthetic plastic polymer. Silicone can be used to make malleable rubber-like items, hard resins, and spreadable fluids.
We treat silicone as a plastic like any other, given that it has many plastic-like properties: flexibility, malleability, clarity, temperature resistance, water resistance. Like plastic, it can be shaped or formed and softened or hardened into practically anything. But it is a unique plastic because it is much more temperature resistant and durable than most plastics and has a low reactivity with chemicals. And while water resistant, it is also highly gas permeable, making it useful for medical or industrial applications where air flow is required. It's also easy to clean, non-stick, and non-staining, making it popular for cookware and kitchen utensils.
So what exactly are silicones (or siloxanes, as their backbone chemical structure is called)?
Many people seem to think they are a natural material derived directly from sand. Not so.
Like any plastic polymer, silicones are synthetic and include a mix of chemical additives derived from fossil fuels. The key difference from the common carbon-based plastics we describe here is that silicones have a backbone made of silicon. It’s important to get the terminology right here, and there are three distinct related substances to understand:
- Silica: When people say silicones are made of sand, they are not incorrect, though that’s too simplistic a description. Silica—or silicon dioxide—is what they are referring to. Silica is the raw material used to make silicone resins. Beach sand is practically pure silica, as is quartz.
- Silicon: This is the base element that makes up silica, but silicon is not generally found in nature in this elemental form. It is made by heating silica at very high temperatures with carbon in an industrial furnace.
- Silicone (siloxane): The silicon is then reacted with fossil fuel–derived hydrocarbons to create the siloxane monomers (alternating silicon + oxygen atoms) which are bonded together into polymers to form the backbone of the final silicone resin. The quality of these silicones can vary greatly depending on the level of purification done. For example, the silicones used to make computer chips are highly purified.
Silicone is often used for baby nipples, cookware, bakeware, utensils, and toys. Silicones are also used for insulation, sealants, adhesives, lubricants, gaskets, filters, medical applications (e.g., tubing), casing for electrical components.
Is Silicone Safe?
Many experts and authorities consider silicone completely safe for food use. For example Health Canada states: "There are no known health hazards associated with use of silicone cookware. Silicone rubber does not react with food or beverages, or produce any hazardous fumes."
Scientific American reports that in 1979 the US Food and Drug Administration determined silicon dioxides—the raw material for silicone products—were safe for food-grade applications. However, the first silicone cookware only appeared a decade later (e.g., spatulas) and no follow-up studies were done to assess whether silicone cookware leaches anything potentially harmful.
The fact is, there has not been a lot of research done to date on the health effects of silicone.
Nonetheless, our own research and review of peer-reviewed scientific studies that have been done indicates we should begin to be cautious about silicone.
Here are some highlights:
- Silicones are not completely inert or chemically unreactive and can release toxic chemicals. They can leach certain synthetic chemicals at low levels, and the leaching is increased with fatty substances, such as oils.
- One study tested the release of siloxanes from silicone nipples and bakeware into milk, baby formula and a simulant solution of alcohol and water. Nothing was released into the milk or formula after six hours, but after 72 hours in the alcohol solution several siloxanes were detected.
- Another study found siloxanes being released from silicone bakeware, with leaching increasing as the food fat content increased.
- A review of the literature indicated that the key critical effects of common siloxanes, as shown in animal studies, are impaired fertility and potential carcinogenicity (2005 Report by the Danish Ministry of the Environment: Siloxanes - Consumption, Toxicity and Alternatives).
- The European Union considers certain siloxanes to be endocrine disruptors (Study on enhancing the Endocrine Disruptor priority list with a focus on low production volume chemicals, ENV.D.4/ETU/2005/00w28r)
- Silicone tubing commonly used for medical applications has been shown to leach several chemicals, including dioctyl phthalate (2006 study in International Journal of Pharmaceutics: Extractables/leachables from plastic tubing used in product manufacturing)
- Silicone intravenous devices have been shown to leach silicone and cause local inflammation (1999 Study in Archives of Disease in Childhood: Plastic migration from implanted central venous access devices)
Low recycling rate.
Silicone does not biodegrade or decompose (certainly not in our lifetimes). Silicones are very persistent in the environment.
Silicones are recyclable, but not likely through your local municipal recycling program. You likely would have to take them to a specialized private recycling facility. Such specialized recycling companies will typically down-cycle it into oil used as lubricant for industrial machines.
Relatively safe. But silicone is not as inert, stable and chemically unreactive as many claim. Use with caution, and if you can find an alternative, use it.
As you can see from our product line, we carry a number of items that contain silicone, usually in the form of seals or gaskets. Silicone has become a standard high quality seal for products requiring an airtight watertight seal, and a suitable alternative has not yet become available. Natural rubber can be a good alternative for things like soothers and bottle nipples, as long as there is no risk of rubber allergy.
For now, we are comfortable continuing to carry products that have high quality, food grade or medical grade silicone parts. We balance the toxicity information stated above with the knowledge that silicone is a high quality, relatively stable material, and leaching of chemicals from other plastics is of much greater concern.
Some basic tips for safe silicone use:
If you are going to use silicone, be sure it is high quality, food grade or medical grade silicone and does not contain any fillers.
- To test a product for fillers you can pinch and twist a flat surface of it to see if any white shows through. If so, a filler likely has been used. As a result, the product may not be uniformly heat resistant and may impart an odor to food. But most importantly, you will have no idea what the filler is and it may leach unknown chemicals into the food. For all you know, the filler may be a silicone of low quality or not silicone at all.
- Bottle nipples and pacifiers should be safe, but best not to put them in the dishwasher, and if they get cloudy or worn out, replace them (ideally, they should be replaced every six to eight weeks). Natural rubber is another option, as long as your child does not have an allergy to natural rubber latex.
We feel uneasy about silicone cookware.
- While silicone is durable and has a high temperature resistance, it makes us queasy to be heating food to very high temperatures in a material like silicone which has been shown to leach chemicals and is not completely inert and stable.
- There are excellent glass, ceramic and stainless steel options for cooking and baking. Yes, we do consider silicones a safer alternative to Teflon and similar non-stick cookware that may have perfluorinated chemicals, but we would opt to use it only when there is really no other choice. We just don’t like the idea of it being subjected to such extreme temperatures while in direct contact with food (often oily food).
- Things like silicone oven mitts, utensils (spatulas, spoons), splatter guards and pot holders should be fine given the minimal amount of time they are in contact with food. But again, we prefer to avoid them for direct food use where possible. We get rather queasy about leaving a silicone spoon soaking in a simmering batch of tomato chili, or a spatula flipping burgers on a hot, oily griddle or flaming barbecue.