β,4-dimethylcyclohex-3-ene-1-propan-1-al

Endpoint summary

Description of key information

Skin sensitisation: Skin sensitiser 1B based on testing in an OECD TG 429 and an extrapolated EC3 of 22.8%

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (sensitising)

Additional information:

A LLNA study was performed to assess the skin sensitisation potential of limoxal in mice following topical application of 25µl of 25%, 50% or 100% of limoxal in acetone/olive oil 4:1 to the dorsal surface of the ear. No signs of systemic toxicity were noted. The SI were 3.73, 4.18 and 8.26 for 25%, 50% and 100% respectively. These values shows an EC3 of <25%.

In addition, in silico, in chemico, in vitro and two other in vivo studies are available investigating the sensitizing potential of Limoxal.

• In silico: A Derek Nexus assessment yielded a skin sensitisation alert for aldehyde and terpenoid and predicted an EC3 of 4.8% and 12%, respectively. When run in the OECD toolbox, alerts were found in protein binding (OASIS v1.1 and OECD) and protein binding alerts for skin sensitization. The chemical structure of this material is predicted to react directly with skin proteins via Schiff base.


• In chemico: The test item was concluded as a non-sensitiser with low reactivity in Direct Peptide Reactivity Assay (DPRA) performed similar to the OECD 442C Guideline.


• In vitro: Several in vitro studies are available. The induction of Antioxidant-Response-Element Dependent Gene Activity in the Keratinocyte ARE-Reporter Cell Line KeratinoSens Assay was conducted to determine the skin sensitization potential of limoxal similar to OECD 442D and found to be positive. Limoxal also induces dendritic cell activation in the human cell-line activation test (h-CLAT) conducted similar to OECD 442E.


• In vivo: Two additional LLNA studies were conducted to assess the skin sensitization potential of limoxal. In a follow up test of the key study using the same concentrations, SI values of 1.8, 4.23 and 3.89 were found, resulting in an EC3 of 37.35%. In the third test, no effects were observed at and up to 50% (highest dose tested).

Based on the data available, Limoxal is considered to be a skin-sensitizer.

EC3 derivation: For calculating the EC3, the EC3 of <25% from the LLNA study was used. The EC3 values of 4.8% and 12% predicted by Derek Nexus assessment is considered very conservative because of the availability of two LLNA studies in which the EC3 is found to be between <25 and 37%, respectively and one study not showing sensitisation up to 50%. Therefore, data from the key LLNA study (EC3 <25%) was extrapolated using linear extrapolation resulting in an EC3 of 22.8%.

Justification for classification or non-classification

The substance is a skin sensitiser based on several in silico, in chemico, in vitro and in vivo data and therefore needs to be classified as a skin sensitiser category 1B (May cause an allergic skin reaction, H317) according to EU CLP (EC No. 1272/2008 and its amendments).