Cyclotetrasiloxane (D4)
The question

Is Cyclotetrasiloxane (D4) safe in deodorant?

AvoidDeodorant

A volatile cyclic silicone that the EU has prohibited outright in cosmetic products (Annex II), primarily on environmental persistence grounds; its rodent reproductive effects appear species-specific rather than human-relevant, but the regulatory prohibition makes it one to avoid on a label.

What the research flags

  • The EU has added D4 to Annex II of the Cosmetics Regulation — the list of substances prohibited in cosmetic products — as entry 1388 (Commission Regulation (EU) 2019/831), so it is banned outright in EU cosmetics, not merely restricted
  • The EU Risk Assessment Committee concluded that D4 meets the REACH criteria for a persistent, bioaccumulative and toxic (PBT) substance and a very persistent, very bioaccumulative (vPvB) substance, and it was separately restricted from wash-off cosmetic products at 0.1 percent or more by weight since 31 January 2020 (EU Regulation 2018/35)
  • Reproductive effects observed in rodent studies arise from a rat-specific delay of the mid-cycle gonadotrophin-releasing-hormone surge that is not relevant to human reproduction, so on this mode-of-action analysis D4 should not be classified as a CMR substance or an endocrine disruptor (Andersen 2022, PMID 34995712)
  • A weight-of-evidence, biochemical and molecular-docking analysis found the estrogenic endocrine-disruptive potential of D4 to be molecularly, biochemically and physiologically implausible (Borgert 2025, PMID 39976757)

Regulatory
IARC Class: NL

Other deodorant ingredients on file

Sources & references

  1. [1]
    RegulatoryInternational regulator — TXT
  2. [2]
    RegulatoryInternational regulator — TXT
  3. [3]
    Peer-reviewedPubMed / NCBI — pubmed.ncbi.nlm.nih.gov · ref 34995712
  4. [4]
    Peer-reviewedPubMed / NCBI — pubmed.ncbi.nlm.nih.gov · ref 39976757

Research disclaimer: Ratings reflect peer-reviewed research and regulatory assessments available at the time of publication, not the dose or formulation of any specific deodorant product. This is not medical advice.