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Description of key information

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (not sensitising)
Additional information:

Animal information

In a study to evaluate the skin sensitization potential of methylionone tests like the guinea pig maximization test (GPMT), open epicutanous test (OET), the Draize-Test and Freund’s Complete Adjuvant Test (FCAT) with guinea pigs were compared (Klecak, 1977). For the GPMT, male and female outbred Himalayan guinea pigs were injected intradermally two times with 0.1 ml of 5% methylionone with and without Freund's complete adjuvant (FCA) on day 0. In addition, 250 mg test material dissolved in petrolatum at 25% concentration was applied on day 8 under occlusion for 48 hours to a clipped area of the neck. The Challenge on day 21 was via a 24 hour closed patch at subirritant concentration.  The reading at 24 and 48 hours after removing the patch revealed no sensitizing effects.

The OET was conducted using 6-8 male and female outbred Himalayan guinea pigs while the same number of untreated animals was used as controls (Klecak, 1977). The induction was via 21 daily open applications of 0.1 ml of 100% methylionone to an 8 cm2 area on the clipped flank skin of the animals. The challenge was conducted on days 21 and 35 via open application of 25 µl of a concentration of 100% methylionone to the contralateral flank of the animals. Evaluation of the sites at 24, 48 and 72 h after challenge revealed no sensitizing effects.
The Draize test was conducted using male and female outbred Himalayan guinea pigs (Klecak, 1977). 0.05 ml of 0.1% methylionone in normal saline was injected intradermally on day 0 followed by 0.1 ml injection on 9 alternate days for a total dose of 0.95 mg. A following intradermal challenge dose of 0.05 ml was given on days 35 and 49. The evaluation criterion was the mean diameter of the papular reactions. As a result, no sensitization to skin was detected.

The Freund's complete adjuvant test (FCAT) was conducted using male and female outbred Himalayan guinea pigs (Klecak, 1977). The induction was performed via 5 intradermal injection of 0.1 ml of a 50:50 mixture of methylionone and FCA into the neck of the animals on days 0, 2, 4, 7 and 9. The control animals were similarly treated with 5 x 0.05 ml of FCA alone. The challenge was via a 24 hour closed patch applied to the flank of test and control animals at subirritant concentration on days 21 and 35. No sensitizing effect was detected.

In another study by the same author (Klecak, 1985), the basic scope and limits of the FCAT and the OET were comparatively discussed. Within a table, the author summarized the predictive value of the OET compared to human tests such as the Human Maximization Test (HMT) and the Repeat Insult Patch Test (RIPT) for a total of 290 substances including methyl ionone.

For methyl ionone, the result of the OET testing with guinea pig was compared to that of the HMT reported by Kligmann AM (1966). The OET was conducted with 6 male and femal guinea pigs which received 21 dermal applications of 0.1 ml methylionone on an area of 8 cm2 on the flank in 21 days or 20 applications in 28 days. The challenge consisted of two applications on days 21 and 35 and evaluation was done 24 and 48 later. No sensitizing effects were detected.

In another study of the same author (Klecak, 1979), also an OET was conducted using 6-8 male and female outbred Himalayan guinea pigs while the same number of untreated animals was used as controls. Induction consisted of 21 daily open applications of a 0.1-ml aliquot of the test material to an 8 cm2 area on the clipped flank skin of the animals. The reactions were read after 24 hours. The challenge was conducted on days 21 and 35 via open application of 25 µl of a concentration of 10% methylionone to the contralateral flank of the animals. Evaluation of the sites at 24, 48 and 72 h after challenge revealed no sensitizing effects.

Another study reported two test versions of mouse ear swelling essay (MESA) which were non-invasive and utilized only topical abdominal dosing and ear challenge with single applications (Thorne, 1991). Vit A was different from the regular MESA only in that mice were maintained on a diet with 17-fold higher levels of vitamin A acetate beginning three weeks prior to induction. For the induction, undiluted solution F-22 containing 6.8% methyl ionone and methyl isoeugenol was applied to the epilated abdomen of Balb/c mice. The challenge was via one application of F-22 to the ears followed by evaluatuion of the ear thickness increase (ETI) after 24, 48 and 72 h. A significant ear swelling was defined as an ETI exceeding the upper confidence bound defined in a previous irritation dose-response study. As a result, F-22 was positive in the vit A MESA assay but negative in the MESA assay.

Another GPMT was described in a Japanese publication and used concentrations of 10% of methylionone for induction and challenge. As result, no sensitizing effects were reported (Ishihara. 1986).

Human information

In addition to the studies with animals, three reports of testing methylionone in humans were available.

In one study, a Kligman maximization test was used to study 20 test materials commonly used in fragrance formulations in 25 healthy adult volunteers (Greif, 1967). The substances including methylionone were applied at 10% under occlusion to the same site on the forearms of all subjects for 5 alternate-day 48 hour periods. Thereby, the patch sites were pre-treated for 24 hours with 1 ml of 5% aqueous sodium lauryl sulfate under occlusion. Following a 10 day rest period, a challenge patch of the test material at a concentration of 10% was applied to a fresh site on the scapular back for 48 hours under occlusion. Prior to challenge, 10% sodium lauryl sulfate was applied to the test site for one hour before application of test material. The challenge site was read at patch removal and again on each of two successive days. Methylionone was found to be not sensitizing when applied to human skin.

In another study with human, 42 out of 4737 Japanese volunteers were treated with 0.05 to 0.5% of methylionone in a perfumed and non-perfumed cream base as vehicle at the same time (Takenaka, 1986). The application was via a piece of 1 cm2 lint covered with cellophane disc placed held by plaster placed on the back, the forearm and the inside of the upper arm. After 24 h the patches were removed and sites were evaluated for erythema and edema.  For methylionone no sensitizing effects were reported.

The same negative result was found in a study, where 20 male and female patients with different dermatoses were tested with concentrations of 1%, 10% and 100% methylionone in olive oil. No time schedule was given, but application sites were examined every two or three days for several weeks after patch removal. No sensitizing effects in the 20 subjects were reported.

In summary, the studies with guinea pigs as well as studies with human showed, that methylionone did not induce sensitizing effects when applied to skin. Although one showed a positive reaction, the tested substance contained other fragrance ingredients than methylionone and the ear swelling test is not regarded as reliable compared to other tests available. Therefore this result was not taken into assessment.


Migrated from Short description of key information:
Sensitization:
- Skin: not sensitizing (Guinea pig; GPMT, OET, FCAT, Draize)

Justification for classification or non-classification

The present data on skin sensitisation do not fulfill the criteria laid down in 67/548/EEC and 1272/2008/EEC, and therefore, a non-classification is warranted.