While the types of silicone used in silicone-based lube have so far been shown to be safe for cosmetic use from a health standpoint, there are lingering questions as to their environmental friendliness.
Because they don’t get absorbed, like water-based creams do, silicones stay on the skin - or, in the case of lube, inside the body - until they get physically washed off, making their way down the drain. And given the widespread use of silicones in personal care products these days, the worry is the extent to which these chemicals end up accumulating in the environment and harming aquatic ecosystems.
If you haven't already, make sure to check out my post about silicone-based lube where I explain the different types of silicones. |
Silicones are non-biodegradable... but they nonetheless degrade relatively quickly and naturally on their own
Silicones get a lot of pushback for being “non-biodegradable”, but this doesn’t necessarily mean that they are environmentally toxic. As cosmetic chemist and science educator Lab Muffin explains:
Biodegradable" means that something can be broken down by living things (e.g. bacteria). But non-biodegradable doesn’t mean that something is bad. For example, glass is non-biodegradable, but it’s inert and non-toxic, therefore it isn’t a big issue. Silicones, on the other hand, aren’t biodegradable, but they are degradable – they degrade in the environment, and turn back into silica (sand), carbon dioxide and water.
She also notes that the majority of washed off dimethicone (a common type of silicone in lube) gets removed in wastewater treatment. Rather than dissolving in water, it naturally sticks to clay or sediment where it degrades on its own. The Derm Review echoes this, stating that "[c]lay filtration of dimethicone and [other] silicones degrades the silicone and is a natural chemical-free way to prevent silicones from entering the environment."
This process usually takes less than 2 years, which means dimethicone technically gets categorized as “persistent” but, compared to plastics for example, dimethicone (and its close relative dimethiconol) degrade remarkably quickly. Meanwhile, the other family of silicones commonly used in lube, called cyclomethicones, mostly evaporates with the help of sunlight and oxygen. Lab Muffin says that half of them will degrade in this way within 2 weeks.
Bioaccumulation: a complicated mix of misunderstandings, theories and facts
The build-up of silicones in the bodies of humans, birds and marine organisms is frequently cited as a problem with using silicones in wash-off care products. However, a number of sources (e.g. the Derm Review and others have rejected the idea that silicones bioaccumulate in humans, asserting that “their size prevents them from being able to pass through cell membranes, a key requirement for bioaccumulation.” This is also why silicones can't enter the bloodstream.
Meanwhile, this review of the persistence, bioaccumulation and toxicity of silicones suggests that lab findings of silicone bioaccumulation in aquatic organisms are inconclusive and that any potential bioaccumulation that might occur is currently unproblematic. As for birds, this same review has determined that they're even less at risk of bioaccumulation than humans.
Official regulations & restrictions
Given the relatively low concentration of these compounds in the environment, there is a pretty clear global consensus that silicones are safe, with large-scale assessments having been conducted in various countries, including Japan, Canada, Australia, and the US.
Only in the EU have the potential long-term environmental effects of the cyclomethicones D4 and D5 prompted authorities to take precautionary action, restricting the amount of these silicones in wash-off personal care products to <0,1% as of January 31, 2020. They're also registered on the REACH annex XVII restricted substances list by the EU Commission Regulation, and are identified by the European Chemicals Agency as persistent, bioaccumulative and toxic.
However, Lab Muffin highlights an important difference about how the EU makes decisions about substance restrictions, noting:
The difference in the regulation between regions comes from Europe’s use of the precautionary principle, which means they focus on laboratory studies and the potential for harm over environmental evidence when making safety assessments.
The debate continues
Various parties are invested in claiming either the safety or hazards of silicones, which means that more research is being done. The US Environmental Protection Agency, for one, is currently undertaking a big evaluation of the possible health and environmental repercussions of D4 (the most controversial cyclomethicone).
If new evidence arises, some of us may want to reassess our lube preferences. But, in the meantime - as always - do what you will with what we know so far.
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