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Skin sensitisation

Link to relevant study records
skin sensitisation: in vivo (LLNA)
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Guideline-conform study under GLP without deviations
according to guideline
OECD Guideline 429 (Skin Sensitisation: Local Lymph Node Assay)
GLP compliance:
Type of study:
mouse local lymph node assay (LLNA)
Details on test animals and environmental conditions:
- Source: Harlan Laboratories B.V., Postbus 6174, 5960 AD Horst / The Netherlands
- Age at study initiation: 8 - 11 weeks
- Weight at study initiation: 19.2 - 24.5 g
- Housing: group caging
- Diet: pelleted standard diet (Harlan Laboratories B.V., 5960 AD Horst, The Netherlands), ad libidum
- Water: tap water, (Gemeindewerke, 64380 Rossdorf, Germany), ad libitum
- Acclimation period: At least 5 days prior to the start of dosing under test conditions after health examination. Only animals without any visible signs of illness were used for the study

- Temperature (°C): 22 + 2°C
- Humidity (%): 45-65 %
- Photoperiod (hrs dark / hrs light): artificial light 6:00 a.m. - 6:00 p.m.
- Bedding: granulated soft wood bedding (Rettenmaier & Söhne GmbH + Co. KG, 73494 Rosenberg, Germany)

acetone/olive oil (4:1 v/v)
5%, 10% and 17% (w/w)
No. of animals per dose:
Details on study design:

A solubility experiment was performed according to the recommendations given by OECD 429. The highest test item concentration, which could be technically used was a 10% suspension in propylene glycol. At higher concentrations, an applicable formulation of the test item was not achieved, neither by the use of other vehicles nor by using additional methods to formulate the test item (e.g. vortexing, sonicating, warming to 37°C).
To determine the highest non-irritant test concentration that does at the same time not induce signs of systemic toxicity, a non-GLP irritation pre-test was performed in two animals. Two mice were treated by (epidermal) topical application to the dorsal surface of each ear with test item concentrations of 5% and 10% (w/w) once daily each on three consecutive days. Prior to the first application of the test item and before sacrifice the body weight was determined. Clinical signs were recorded at least once daily. Eventual signs of local irritation were documented and a score was used to grade a possible erythema of the ear skin. Furthermore, prior to the first application of the test item (day 1), on day 3 and before sacrifice (day 6) the ear thickness was determined using a micrometer. Additionally, for both animals, the ears were punched after sacrifice (day 6) at the apical area using a biopsy punch (Ø 8 mm corresponding to 0.5 cm2) and were immediately pooled per animal and weighed using an analytical balance. Eventual ear irritation was considered to be excessive if an erythema of the ear skin of a score value ≥3 was observed at any observation time and/or if an increase in ear thickness of ≥25% was recorded on day 3 or day 6. The measured ear weight was also considered in this evaluation.
There were no signs of systemic toxicity or excessive local skin irritation. Eventual erythema formation could not be assessed due to the colour of the test item, but increase in ear thickness and ear weights were below the threshold value of ≥25% increase compared to pre-treatment values (for ear thickness) and historical vehicle values (for ear weights), respectively. For further details of this irritation pre-test, see Appendix 1 of the report.
The test item in the main study was therefore assayed at the concentrations 2.5%, 5% and 10% (w/w). The highest concentration tested was the highest level that can be achieved whilst avoiding systemic toxicity and excessive local irritation as confirmed in the pre-experiment described above. The subsequent concentrations correspond to the concentrations specified by the OECD Guideline 429.


Each test group of mice was treated by topical (epidermal) application to the dorsal surface of each ear (left and right) with different test item concentrations of 2.5%, 5% and 10% (w/w) in propylene glycol. The application volume, 25 µL was spread over the entire dorsal surface (~ 8 mm) of each ear once daily for three consecutive days. A futher group of mice was treated with an equivalent volume of the relevant vehicle alone (control animals).


Five days after the first topical application, all mice were intraveneously injected into a tail vein with radio-labelled thymidine (3HTdR). Approximately five hours after treatment with 3HTdR all mice were sacrificed and the draining lymph nodes were excised and pooled per group. Single cell suspensions of lymph node cells were prepared from pooled lymph nodes, which were subsequently washed with phosphate buffered saline and incubated with trichloroacetíc acid overnight. The proliferative capacity of pooled lymph node cells was determined by the incorporation of 3H-methyl thymidine measured in a ?-scintillation counter.


The proliferation response of lymph node cells is expressed as the number of radioactive disintegrations per minute per lymph node (DPM/node) and as the ratio of 3HTdR incorporated into lymph node cells of test lymph nodes relative to that recorded for control lymph nodes (stimulation index). Before DPM/node values were determined, mean scintillation-background DPM was subtracted from test and control raw data. A test item is regarded as a sensitiliser in the LLNA if the following criteria are fulfilled:
-First, that exposure to at least one concentration of the test item resulted in an incorporation of 3HTdR at least 3-fold or greater than that recorded in control mice, as indicated by the stimulation index.
-Second, that the data are compatible with a conventional dose response, although allowance must be made (especially at high topical concentrations) for either local toxicity or immunological suppression.


In addition to the sensitising reactions the following observations and data were recorded during the test and observation period:
Mortality / Viability: At least once daily from experimental start to necropsy.

Body weights: In the pre-test: prior to the first application and prior to sacrifice. In the main experiment: prior to the first application and prior to treatment with 3HTdR.

Ear thickness: In the pre-test prior to the first application of the test item (day 1), on day 3 and before sacrifice (day 6).

Ear weights: In the pre-test after sacrifice; biopsy punches were taken from each ear.

Clinical signs (local / systemic): Clinical signs (local irritation at the application site or systemic toxicity) will be recorded at least once daily. Especially the treatment sites will be observed carefully.

Positive control substance(s):
hexyl cinnamic aldehyde (CAS No 101-86-0)
The mean values and standard deviations were calculated in the body weight tables.
Positive control results:
Experiment performed in October 2012 (Harlan study number 1510201) using concentrations of 5, 10, and 25 % alpha-hexyl cinnamic aldehyde in acetone:olive oil (4:1). These concentrations yielded S.I.´s of 1.5, 1.9, and 5.7, respectively.
The EC3 value calculated was 14.3 % (w/v).
The positive control substance alpha-hexyl cinnamic aldehyde was found to be a skin sensitizer under the described conditions, demonstrating the validity of the study.
Remarks on result:
other: Stimulation Indices (S.I.) of 1.17, 1.29, and 1.26 were determined with the test item at concentrations of 5, 10, and 17 % (w/v) in acetone:olive oil, 4:1 (v/v), respectively
other: disintegrations per minute (DPM)
Remarks on result:
other: see depicted table below
Key result
conc. 5 %
Key result
conc. 10 %
Key result
conc. 17 %
Interpretation of results:
not sensitising
Migrated information Criteria used for interpretation of results: EU
The test item Pigment Red 4 was not a skin sensitiser under the test conditions of this study
Executive summary:

In the study the test item dissolved in Acetone:olive oil, 4:1 (v/v) was assessed for its possible contact allergenic potential.

For this purpose a local lymph node assay was performed using test item concentrations of 5, 10, and 17 % (w/v).

No symptoms of local toxicity at the ears of the animas and no systemic findings were observed during the study period. Due to the intense red colour of the test item local irritation reactions such as ear redness could not be detected.

In this study Stimulation Indices (S.I.) of 1.17, 1.29, and 1.26 were determined with the test item at concentrations of 5, 10, and 17 % (w/v) in acetone:olive oil, 4:1 (v/v), respectively

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

The test item C.I. Pigment Red 4 was found to be a not skin sensitiser in this assay

Value used for CSA: not sensitising

Respiratory sensitisation

Endpoint conclusion
Endpoint conclusion:
no study available
Additional information:

Respiratory sensitisation

The following information is taken into account for any hazard / risk assessment:

Respiratory tract sensitisation:

Substance is not classified for this endpoint. The substance is considered not to exert any sensitizing effects on the respiratory tract; when aerosolized in respirable form, the substance is considered likely to behave like an inert dust.

Non-human information: This information is not available.

Justification for classification or non-classification

Pigment Red 4 did not show skin sensitising properties in LLNA study with mice.

It can reasonably be deduced that Pigment Red 3 does not cause respiratory tract sensitization and thus does not have to be classified according to the criteria laid down in the EU Dangerous Substances Directive (67/548/EEC) and in the EU Classification Labelling and Packaging Regulation (1272/2008/EC), because

- Pigment Red 4 did not cause skin sensitization, and

- it is unlikely that Pigment Red 4 can interact with the immune system due to its extremely low solubility in water and n-octanol.