Siloxanes L3, L4 and M3T: towards harmonized classification under CLP
Linear siloxanes L3 (Octamethyltrisiloxane), L4 (Decamethyltetrasiloxane) and M3T (Methyl trimethicone) are at the center of a significant regulatory development.
These substances are widely used in cosmetic formulations, including hair care, skin care and make-up, where they function as emollients and conditioning agents, improving spreadability, texture and sensory performance.
Following their inclusion in the ECHA Candidate List as substances of very high concern (SVHC) due to their vPvB properties (very Persistent, very Bioaccumulative), the linear siloxanes L3, L4 and M3T are expected to be included in Annex VI of the CLP Regulation through the new “ATP transfer” mechanism established by Regulation (EU) 2024/2865, which introduced specific provisions to facilitate harmonized classification of substances identified as SVHCs due to PBT/vPvB or endocrine-disrupting properties.
Implications for the cosmetic sector
Inclusion in Annex VI does not automatically restrict use, but it entails significant regulatory consequences. For registrants under REACH, this inclusion:
- may require updates to the Chemical Safety Report (CSR), originally submitted as part of the REACH registration dossier.
- will require the revision of exposure scenarios, and alignment of classification and labelling.
The main challenge in cosmetics lies in demonstrating safe use, as these applications are considered wide dispersive uses, characterized by:
- environmental release after use;
- widespread and difficult-to-control exposure;
- limited control of exposure pathways.
For vPvB substances, these conditions significantly complicate safety assessment, affecting both CSR and Cosmetic Product Safety Reports (CPSR). As a result, maintaining use becomes increasingly challenging, while regulatory pressure is expected to intensify over time.
A further critical element is the lack of fully equivalent alternatives for certain applications,particularly in make-up, which may impact formulation continuity and supply chains.
Regulatory status
The inclusion process in Annex VI is implemented via the “ATP transfer”, a new mechanism still under operational development. Current regulatory attention is focused on L3, L4 and M3T, while L2 and L5 are outside the scope.
The procedure is expected to progress within the 2026 regulatory cycle, with discussions ongoing within CARACAL and transitional periods under consideration.
Regulatory outlook for cosmetics
The evolving framework confirms a progressive tightening for SVHC substances, particularly those with vPvB properties. In this context, the anticipated inclusion of L3, L4 and M3T in Annex VI is expected to increase regulatory scrutiny on cosmetic uses.
Note on cyclic siloxanes
Unlike the linear siloxanes, the cyclic siloxanes D4, D5, and D6 (identified as SVHCs since 2018) are already subject to well-established REACH restrictions: D4 has been banned in cosmetics since 2019 (CPR II/1388), while D5 and D6 will be limited to <0.1% by weight in all cosmetic products from 6 June 2027 (REACH Annex XVII/70, as amended by Regulation 2024/1328), with industrial restrictions applying from 6 June 2026.
>>> Complife supports economic operators in the transition towards new CLP and REACH requirements. Through testing services and strategic consulting, we assist companies in formulation assessment and compliance management, ensuring product continuity on the European market.
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