Menthol

Endpoint summary

Description of key information

Menthol isomers were tested for skin irritation in rabbits according to the current OECD-guideline 404. All isomers were tested undiluted and in 50, 25, 5 and 1% concentrations. Diethylphthalate (DEP) was used as diluent. The investigations were performed in the same laboratories, using the same protocol.
Menthol in diethylphahtalate (DEP) was tested for eye irritation according to the current OECD-guideline 405.

Key value for chemical safety assessment

Skin irritation / corrosion

Link to relevant study records

Reference

Endpoint:

skin irritation: in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: well documented and scientifically acceptable

Qualifier:

according to guideline

Guideline:

OECD Guideline 404 (Acute Dermal Irritation / Corrosion)

Principles of method if other than guideline:

The day before the experiment was started the rabbits were weighed and an area of 10 x 10 cm on the back was clipped as closely as possible with an electric clipper.
On the experimental day the rabbits were physically restrained on a test table, and the backs were treated on six different fields: Two anterior treatment sites, two centrally located test sites and two posterior treatment sites. To each of the fields about 0.5 ml of one of the test concentrations was applied and covered with gauze packs, 2.5 x 2.5 cm. The gauze packs were secured with a cross of 1 cm wide adhesive tape and fixed with Scanpor tape, 7.5 cm width, loosely wound round the trunk. Five test concentrations were used: 100%, 50%, 25%, 5%, or 1%.
After an exposure time of 4 hours the tape and packs were removed and the related skin was cleaned with soap and lukewarm water. The skin reactions were read.

GLP compliance:

yes

Specific details on test material used for the study:

OTHER SPECIFICS: Name of the test substance as cited in the report: Menthol rac.

Species:

rabbit

Strain:

Himalayan

Type of coverage:

semiocclusive

Preparation of test site:

shaved

Vehicle:

other: diethylphthalate (DEP)

Controls:

not required

Duration of treatment / exposure:

4 hours

Observation period:

4.5, 24, 48, and 72 hours, 7, and 14 days

Number of animals:

4 female rabbits

Irritation parameter:

erythema score

Basis:

mean

Time point:

24/48/72 h

Score:

3

Max. score:

4

Reversibility:

not fully reversible within: 14 days

Remarks on result:

other: undiluted material

Irritation parameter:

edema score

Basis:

mean

Time point:

24/48/72 h

Score:

3

Max. score:

4

Reversibility:

not fully reversible within: 14 days

Remarks on result:

other: undiluted material

On day 7, all sites treated with a 100% concentartion wer covered with a massive layer of white-brown

seales on three test animals and the test site ofone test animal was covered with a thin

layer of white scales. Sites treated with a 50% concentration showed white scales on all rabbits. The test

sites, treated with a 25% concentration showed scattered white scales on one rabbit.

On day 14, the sites treated with a 100% concentration was still covered with white to white-brown

scales, but the underlying skin was intact. The sites treated with a 50% concentration showed scattered

seale formation on intact skin on 3 of the test animals.

Interpretation of results:

Category 2 (irritant) based on GHS criteria

Executive summary:

The day before the experiment was started the rabbits were weighed and an area of 10 x 10 cm on the back was clipped as closely as possible with an electric clipper.

On the experimental day the rabbits were physically restrained on a test table, and the backs were treated on six different fields: Two anterior treatment sites, two centrally located test sites and two posterior treatment sites. To each of the fields about 0.5 ml of one of the test concentrations was applied and covered with gauze packs, 2.5 x 2.5 cm. The gauze packs were secured with a cross of 1 cm wide adhesive tape and fixed with Scanpor tape, 7.5 cm width, loosely wound round the trunk. Five test concentrations were used: 100%, 50%, 25%, 5%, or 1%.

After an exposure time of 4 hours the tape and packs were remoced and the treated skin was cleaned with soap and lukewarm water. The skin reactions were read.

With the undiluted test substance menthol was irritating to the skin (erythema sore: 3 and and edema score: 3). The undiluted compounds were irritating to the skin. Dilution of the compounds led to a pronounced decrease in the irritating properties of the

compounds. No skin reaction at all were observed for D-menthol and menthol liquid at 5 % dilution and for L- and D/L-menthol at 1 % dilution.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (irritating)

Eye irritation

Link to relevant study records

Reference

Endpoint:

eye irritation: in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: well documented and scientifically acceptable

Qualifier:

according to guideline

Guideline:

OECD Guideline 405 (Acute Eye Irritation / Corrosion)

Principles of method if other than guideline:

About 0.1 ml of the test article solution or vehicle was placed in the left or right eye, respectively, of each rabbit by gently pulling the lower lid away from the eyeball to form a cup into which the test substance was dropped. The lids were then gently held together for about one second. The eyes were examined and the grade of ocular reaction was recorded 1 hour later. 24 hours later an examination was performed before and after installation of oculoguttae flouresceini. After the examination the eyes were rinsed with 20 ml of a 0.9% sodium chloride solution.
The eyes were also examined 48 and 72 hours after the treatment, as well as on day 7.

GLP compliance:

yes

Specific details on test material used for the study:

OTHER SPECIFICS: The test substance (Menthol racemic) was used in a test concentration of 40 % (60 % vehicle)

Species:

rabbit

Strain:

Himalayan

Vehicle:

other: diethylphthalate (DEP)

Controls:

not required

Duration of treatment / exposure:

24 hours

Observation period (in vivo):

up to 7 days

Number of animals or in vitro replicates:

4 female rabbits

Irritation parameter:

cornea opacity score

Basis:

mean

Time point:

24/48/72 h

Score:

1

Max. score:

4

Reversibility:

fully reversible

Remarks on result:

other: test substance

Irritation parameter:

iris score

Basis:

mean

Time point:

24/48/72 h

Score:

0

Max. score:

2

Remarks on result:

other: test substance

Irritation parameter:

conjunctivae score

Basis:

mean

Time point:

24/48/72 h

Score:

2.1

Max. score:

3

Reversibility:

fully reversible

Remarks on result:

other: test substance

Irritation parameter:

chemosis score

Basis:

mean

Time point:

24/48/72 h

Score:

0.3

Max. score:

4

Reversibility:

fully reversible

Remarks on result:

other: test substance

Irritation parameter:

cornea opacity score

Basis:

mean

Time point:

24/48/72 h

Score:

1

Max. score:

4

Reversibility:

fully reversible

Remarks on result:

other: vehicle

Irritation parameter:

iris score

Basis:

mean

Time point:

24/48/72 h

Score:

0

Max. score:

2

Remarks on result:

other: vehicle

Irritation parameter:

conjunctivae score

Basis:

mean

Time point:

24/48/72 h

Score:

1.9

Max. score:

3

Reversibility:

fully reversible

Remarks on result:

other: vehicle

Irritation parameter:

chemosis score

Basis:

mean

Time point:

24/48/72 h

Score:

0.3

Max. score:

4

Reversibility:

fully reversible

Remarks on result:

other: vehicle

Moderate to intense reactions of cornea (diffuse areas of opacity) and conjunctiva (redness, swelling and discharge) were seen in all the rabbits at the 1-, 24-, 48- and 72-hour readings, after treatment with the test article and the vehicle. No reaction was seen in iris. No reactions were seen in any of the rabbits on day 7. As it can be seen from the data, the test article formulation and the vehicle had almost the same eye-irritating potential.

Interpretation of results:

Category 2 (irritating to eyes) based on GHS criteria

Executive summary:

About 0.1 ml of the test article solution or vehicle was placed in the left or right eye, respectively, of each rabbit by gently pulling the lower lid away from the eyeball to form a cup into which the test substance was dropped. The lids were then gently held together for about one second. The eyes were examined and the grade of ocular reaction was recorded 1 hour later. 24 hours later an examination was performed before and after installation of oculoguttae flouresceini. After the examination the eyes were rinsed with 20 ml of a 0.9% sodium chloride solution. The eyes were also examined 48 and 72 hours after the treatment, as well as on day 7.

Based on the cornea score = 2.1 a classification as Cat.2, H319 is adequate. However, considering the cornea score = 1.9 of the solvent a classification is not necessary, but taken into account the hole database, a classifiaction as Eye Irrit. 2; : C>25% seems adequate.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (irritating)

Additional information

The undiluted compounds were irritating to the skin. Under the experimental conditions the mean score for erythema and edema was 3.

The test article formulation (menthol as 40% solution in DEP as vehicle) and the vehicle (DEP - diethylphthalate) had almost the same eye-irritating potential. Menthol in a 40% solution is therefore not irritating to the eye.

According to the results from the skin irritation key-study a classification as Skin Irrit. 2, H315 (GHS) (erythema and edema score: both 3) is justified.

For eye-irritation according to GHS due to the cornea score = 2.1 a classification as cat.2, H319 is adequate.

Other isomers and concentrations were also studied by the same testing laboratory (from OECD SIDS for menthols, UNEP Publications).

A 29% solution of L-menthol had the following scores: cornea opacity 0.2; redness 0.6; chemosis 0.1.

A 29% solution of D-menthol had the following scores: cornea opacity 0.4; redness 1.3; chemosis 0.4.

Justification for classification or non-classification

Skin irritation: D/L-menthol meets the criteria for classification and labelling for this endpoint, as set out in Regulation (EC) No. 1272/2008. Based on a valid key study performed according to OECD 404 protocol, the substance showed irritating properties with a maximum Draize score of 3 that were reversible although not fully reversed at the highest concentration of 100% but the underlying skin remained intact. At concentrations below 50% menthol, the test data did not meet the criteria for classification as skin irritant. Consequently, a specific concentration limit for skin irritation Category 2 is set to ">25% by weight".

Eye irritation: According to CLP classification criteria (Regulation (EC) No 1272/2008), the substance meets the criteria for eye irritant category 2.

Although 40% L-menthol in DEP when tested showed very slight irritation of the eye; the results from testing 29% D- and L-menthol and 5% L-menthol clearly indicated no need for classification applying CLP criteria. Consequently, a specific concentration limit for eye irritation Category 2 is set to ">25% by weight".