As consumers become more wary of the chemicals they’re putting into their bodies, more and more research is coming out about the potential health risks of plastic and plastic alternatives. Here, Jay Sinha and Chantal Plamondon, the couple behind the eco-friendly consumer goods marketplace Life Without Plastic, dive into the pros and cons of a common one: silicone.

Silicones have become enormously popular in recent years and are constantly marketed as safe replacements for traditional plastics. We see them everywhere—baby bottle nipples, utensils, toys, mugs, food containers, seals on bottles and containers. They’re even proudly used in baking sheets and muffin trays that will be subjected to high temperatures for the oven and ice cube molds destined for the freezer.

You’ll also find silicones used in cosmetics and various personal care products to make them soft and smooth. In more industrial contexts, they are commonly used for insulation, sealants, adhesives, lubricants, gaskets, filters, medical applications (e.g., tubing), and casing for electrical components.

Silicones—or siloxanes as they are also known—are something of a hybrid between synthetic rubbers and synthetic plastic polymers. They can take on different forms and be used to make malleable rubberlike items, hard plasticlike resins, and thick spreadable fluids.

We treat silicones as plastics like any other, given that they have plasticlike properties: flexibility, malleability, clarity, temperature resistance, and water resistance. Like plastic, they can be shaped or formed and softened or hardened into practically anything. Since they’re easy to clean, nonstick, and nonstaining, they’re popular for cookware and kitchen utensils, too.

Many people seem to think that silicones 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 all the carbon-based plastics we described above is that silicones have a backbone made of silicon. I know, confusing! It’s important to get the terminology right here, so let’s dive in:

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.

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.

The silicon is then reacted with fossil fuel—derived hydrocarbons to create siloxane monomers that are bonded together into polymers to form the final silicone resin. The quality of these silicones can vary greatly depending on the level of purification. For example, the silicones used to make computer chips are highly purified.

This is the big question, and there is not yet a clear answer. They are very stable polymers with strong temperature and chemical resistance, so we consider them relatively safe. A number of the products we offer in our store, Life Without Plastic—such as stainless-steel or glass food containers and bottles—include silicone seals or gaskets to make them airtight and watertight. At this point, we are not aware of a better durable alternative for such applications, apart from perhaps natural rubber for things like soothers and bottle nipples, as long as there is no risk of rubber allergy.

Many experts and authorities consider silicones to be nontoxic and safe for contact with food and drink. 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.”

Consumer advocate and toxin-free living expert Debra Lynn Daddtakes a cautious view toward silicones and continues to assess new research, but she is not willing to give up her silicone cookware just yet, as she considers it safer than nonstick alternatives with perfluorinated chemical coatings.

While the research indicates that silicones are certainly very stable, they are not completely inert. In other words, there is possibility of leaching. For example, one study tested the release of siloxanes from silicone nipples and bakeware into milk, baby formula, and a 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. Siloxanes are considered potential endocrine disrupters, and some have been linked to cancers.

Siloxanes are also present at detectable levels in land, air, and water, and given their durability, they tend to persist in the environment for a long time.

The upshot is that the scientific evidence is weak in pointing a smoking gun at silicones, but the questions and uncertainty are there, so it’s worth keeping a close eye on them—especially given the growing concerns about endocrine-disrupting chemicals that might produce health problems a generation after a minuscule exposure.

Apart from the health aspects described above, silicone poses an environmental threat because it is rarely recycled. Although silicone products can be collected by specialized recycling companies that will typically down-cycle it into oil used as lubricant for industrial machines, it is rarely accepted in municipal curbside recycling programs. Therefore, just like plastics, not only can silicone only be down-cycled, but most of it just ends up in landfills where it won’t biodegrade for hundreds of years.

Given our precautionary approach, we prefer to avoid silicones when there are better alternatives. That said, here are a few silicone-use tips if you do decide to make them part of your life: