Cyclosiloxanes are chemical compounds that are frequently used in medical devices and in-vitro diagnostics (IVD). Similar to perfluorinated and polyfluorinated alkyl compounds (PFAS), they have been the focus of the European Chemicals Agency (ECHA) for years due to their persistent and bioaccumulative properties. However, unlike PFAS, they have not yet been as much of a focus for manufacturers, although EU regulations will already restrict the use of these substances from 2026. Cause for panic? Let us focus on the most important facts and explain what you need to pay attention to.

What are cyclosiloxanes?

Octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethycyclohexasiloxane (D6): These three substances represent the group of cyclosiloxanes, and are mainly used as plasticizers, solvents, humectants, processing aids, lubricants, release agents, and anti-foaming agents. Cyclic siloxanes are slightly volatile, ring-shaped organic compounds consisting of alternating silicon and oxygen atoms. In addition, two further methyl groups are bonded to the silicon atom.

Cyclic siloxanes are mainly starting products for silicone polymers and are often used in cosmetics and personal care products. In medical devices and IVDs, D4, D5 and D6 are used as coatings for subcutaneous needles, in hydrogels for contact lenses, insulin pumps, and in prostheses, among other things.

The regulatory history

In June 2018, the ECHA Member State Committee (MSC) agreed to classify D4, D5 and D6 as SVHC (Substance of Very High Concern) as they are very persistent and very bioaccumulative (vPvB). Furthermore, it was decided that D4 should also be classified as a persistent, bioaccumulative and toxic substance (PBT = persistent, bioaccumulative and toxic). It was also determined that D5 and D6, if they contain more than 0.1 % by weight of D4 , should also be assessed as PBT substances. In January 2018, the Commission adopted Regulation (EU) 2018/35, which restricted the placing on the market of D4 and D5 in wash-off cosmetic products.

In 2020, the Committee for Socio-Economic Analysis (SEAC) adopted its opinion supporting the restriction of the release of D4, D5 and D6 in order to reduce their emissions to the environment.

In 2021, ECHA recommended to the European Commission to add the cyclic siloxanes to the candidate list, and in 2022 D4 was even listed under the CLP regulation.

Finally, in 2024, Regulation (EU) 2024/1328 was published and, among other things, restricts the use and placing on the market of cyclic siloxanes. This restriction will come into force on June 6, 2026. As a result, D4, D5 and D6 may no longer be placed on the market as a substance, as a constituent of other substances, or in mixtures in a concentration equal to or greater than 0 .1 % by weight.

What transitional periods apply? Are there any exceptions?

Some Member States of the European Union have expressed concerns about the short transition period for medical devices. A search for alternative materials, including a qualification process and the application for registration of a newly designed mixture in accordance with the Medical Device Regulation (EU) 2017/745 (MDR), is difficult to carry out within 2 years. Instead, a 7-year transitional period (until 06.06. 2031) has been defined during which cyclic siloxanes may still be used. The same applies to in-vitro diagnostics.

However, there are also some exceptions where D4, D5, and D6 may continue to be used for medical devices:

• Use of D5, and D6 in medical devices for the treatment and care of scars and wounds, for the prevention of wounds, and for the treatment of stomata
• Use of D4, D5, and D6 as laboratory reagents in research and development activities under controlled conditions
• Use of D4, D5, and D6 in a concentration ≤ 0.2% by weight of the respective substance in the mixture, for use as a medical device or in vitro diagnostic medical device (except In vitro Diagnostic Medical Device Regulation (EU) 2017/746 (IVDR) (6)(d))
• D5 in a concentration ≤ 0.3 % by weight in a mixture or D6 in a concentration ≤ 1 % by weight for use as products within the meaning of Article 1(4) of the MDR for dental impression purposes.

My product contains cyclic siloxanes. Reason to Panic?

If your medical devices contain the cyclic siloxanes D4, D5, or D6, this is no reason to panic immediately. As described above, there are exemption rules and transitional periods during which you as a manufacturer can still react. However, if none of the exemption rules apply to your products, you have no other option than to look for an alternative material.

Otherwise, cyclic siloxanes may be contained in your products in concentrations of up to ≤ 0.2% by weight. We recommend carrying out a toxicological risk assessment (TRA) of the cyclic siloxanes specifically for the medical device of interest and checking - at least by means of a chemical characterization - whether D4, D5, and/or D6 can be dissolved out of the medical device.

We would be pleased to support you in such a risk assessment or as study coordinator of biological tests and in the preparation of a plan and report for the biological assessment. If you have any questions, please contact the author of this article directly or use our contact form.