Research Summary:
Cyclic and linear siloxanes are compounds synthesized from silicon, consisting of alternating atoms of silicone and oxygen [Si-O] units with organic side chains. The most common cyclic siloxanes are octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6), while the most common linear siloxanes are high molecular weight polydimethylsiloxanes (PDMS) and low molecular weight volatile linear siloxanes known as hexamethyldisiloxane (L2), octamethyltrisiloxane (L3), decamethyltetrasiloxane (L4), and dodecamethylpentasiloxane (L5).
These compounds exhibit low dermal toxicity, are generally inert and non-reactive, and are compatible with a wide range of chemicals. They offer beneficial properties such as wash-off or transfer resistance from the skin, sun protection factor (SPF) enhancement, and emolliency in cleaning products. Because of these properties, these compounds are incorporated into multiple consumer products for use on the skin, such as cosmetics and health-care products. Over 300,000 tons are annually sold into the personal care and consumer products sector.
Given their widespread use in consumer products and potential for human dermal exposure, it is crucial to understand the dermal absorption and overall fate of siloxanes following dermal exposure. This review summarizes available data associated with the dermal absorption, penetration, and fate of the most commonly used siloxane substances.
**Keywords**: Siloxanes; dermal; absorption; linear; cyclic; cosmetics; sunscreen products.
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