My sister often complains to me that there are many things in science that have similar names but are completely different. Looking at silicones, I can see what she means. Silicon (without an “e”) is a chemical element. The majority of the Earth crust is made up of minerals that contain silicon – the only element that is more common is oxygen. Silicones (with an “e”) are a different chemical. Silicones made up of siloxanes, which are a combination of silicon and oxygen, with a range of other elements. Because they contain siloxanes, silicones can also be called poly-siloxanes.

There are many types of silicones. They can be liquid or solid, or set after being applied. In personal care products, liquid silicones are used to give smoothness. Silicones are often responsible for the feeling of sleek hair after conditioning, or silky hands after applying moisturiser.

Silicones are not readily biodegradable, but they can break down through other chemical processes. The rate of these reactions is dependent on the environmental conditions. For example, break down is slower under cooler temperatures. Under poor conditions, some silicones can take years to break down in the environment. Because of this, and their chemical characteristics, some silicones can also move through the environment to pollute areas far from their point of release.

Some people choose to avoid silicones for these reasons. Because there is potential for silicones to take years to break down and pollute widespread areas, the use of silicone is sometimes considered to be similar to the use of plastic in terms of environmental concerns.

For particular silicones, there are also concerns around bioaccumulation and aquatic toxicity. Studies have shown that some silicones concentrate in fish tissue, and that they can be very toxic to aquatic invertebrates. Some governments have taken action in response to these types of findings. However, there are still many data gaps. It is important to note that information currently available indicates that these findings are not relevant for all silicones.

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