Hydroquinone

Endpoint summary

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Reference 1

Endpoint:

skin sensitisation: in vivo (non-LLNA)

Type of information:

experimental study

Adequacy of study:

key study

Study period:

no data

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Remarks:

Modified Magnusson and Kligman procedure. The HQ experiment included only 4 animals per group. Challenge applications were open.

Qualifier:

no guideline followed

Principles of method if other than guideline:

In principle the methodology was similar to OECD Guideline 406 (Skin Sensitisation) except the HQ sensitisation assay included a smaller number of animals (4 animals/group) and open application was used at challenge.

GLP compliance:

not specified

Remarks:

publication, University laboratories

Type of study:

guinea pig maximisation test

Justification for non-LLNA method:

Data from a research organization; not originally produced for regulatory purposes.

Species:

guinea pig

Strain:

Dunkin-Hartley

Sex:

female

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: no data
- Age at study initiation: no data
- Weight at study initiation: 400g
- Housing: individual cages
- Diet (e.g. ad libitum): standard solid diet ad libitum (RC-4 oriental Yeast, Osaka, Japan)
- Water (e.g. ad libitum): tap water, ad libitum
- Acclimation period: no data

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 23 +/- 2°C
- Humidity (%): 55 +/- 10°C
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12/12 h light/dark cycle

IN-LIFE DATES: no data

Route:

intradermal and epicutaneous

Vehicle:

other: acetone 80%

Concentration / amount:

On day 0, intradermal injections at 3 different spots:
1) 0.05 ml emulsified mixture of FCA and saline
2) 0.05 ml of 2% hydroquinone in saline
3) 0.05 ml of 2% hydroquinone in emulsified mixture of FCA and saline (1:1)

Route:

epicutaneous, open

Vehicle:

other: acetone 80%

Concentration / amount:

On day 0, intradermal injections at 3 different spots:
1) 0.05 ml emulsified mixture of FCA and saline
2) 0.05 ml of 2% hydroquinone in saline
3) 0.05 ml of 2% hydroquinone in emulsified mixture of FCA and saline (1:1)

No. of animals per dose:

4 females/dose

Details on study design:

MAIN STUDY
A. INDUCTION EXPOSURE
- No. of exposures: 1 intradermal injection on day 0 and one topical application on day 7
- Site: shaved flanks
- Frequency of applications: single application
- Concentrations:
On day 0, intradermal injections at 3 different spots:
1) 0.05 ml emulsified mixture of FCA and saline
2) 0.05 ml of 2% hydroquinone in saline
3) 0.05 ml of 2% hydroquinone in emulsified mixture of FCA and saline (1:1)
On day 7, topical induction with 0.5 g of 1% hydroquinone in petrolatum applied under an occlusive patch for 48 hrs.

B. CHALLENGE EXPOSURE
- No. of exposures: one application
- Day(s) of challenge: day 21
- Exposure period: 24 hrs, open application
- Test groups: hydroquinone in 80% acetone
- Control group: vehicle (acetone at 80% in water)
- Site: flank regions that had been shaved 24h before challenge
- Concentrations: 0.2%, 2% or 20% hydroquinone (0.05 ml containing 0.1, 1, or 10 mg HQ)
- Evaluation (hr after challenge): 24h, 48h, 72 h

Challenge controls:

none

Positive control substance(s):

no

Remarks:

Hydroquinone was the positive control in the study investigating cross-reactivity

Reading:

1st reading

Hours after challenge:

24

Group:

positive control

Dose level:

0.2%

No. with + reactions:

3

Total no. in group:

4

Remarks on result:

other: Hydroquinone was the positive control, see details under test chemical

Reading:

1st reading

Hours after challenge:

24

Group:

negative control

Dose level:

vehicle

No. with + reactions:

0

Total no. in group:

4

Remarks on result:

other: Reading: 1st reading. . Hours after challenge: 24.0. Group: negative control. Dose level: vehicle. No with. + reactions: 0.0. Total no. in groups: 4.0.

Reading:

1st reading

Hours after challenge:

24

Group:

test chemical

Dose level:

0.2%

No. with + reactions:

3

Total no. in group:

4

Remarks on result:

other: Reading: 1st reading. . Hours after challenge: 24.0. Group: test group. Dose level: 0.2%. No with. + reactions: 3.0. Total no. in groups: 4.0.

Reading:

1st reading

Hours after challenge:

24

Group:

test chemical

Dose level:

2%

No. with + reactions:

4

Total no. in group:

4

Remarks on result:

other: Reading: 1st reading. . Hours after challenge: 24.0. Group: test group. Dose level: 2%. No with. + reactions: 4.0. Total no. in groups: 4.0.

Reading:

1st reading

Hours after challenge:

24

Group:

positive control

Dose level:

2%

No. with + reactions:

4

Total no. in group:

4

Remarks on result:

other: Hydroquinone was the positive control, see details under test chemical

Reading:

1st reading

Hours after challenge:

24

Group:

test chemical

Dose level:

20%

No. with + reactions:

4

Total no. in group:

4

Remarks on result:

other: Reading: 1st reading. . Hours after challenge: 24.0. Group: test group. Dose level: 20%. No with. + reactions: 4.0. Total no. in groups: 4.0.

Reading:

1st reading

Hours after challenge:

24

Group:

positive control

Dose level:

20%

No. with + reactions:

4

Total no. in group:

4

Remarks on result:

other: Hydroquinone was the positive control, see details under test chemical

Reading:

2nd reading

Hours after challenge:

48

Group:

negative control

Dose level:

vehicle

No. with + reactions:

0

Total no. in group:

4

Remarks on result:

other: Reading: 2nd reading. . Hours after challenge: 48.0. Group: negative control. Dose level: vehicle. No with. + reactions: 0.0. Total no. in groups: 4.0.

Reading:

2nd reading

Hours after challenge:

48

Group:

test chemical

Dose level:

0.2%

No. with + reactions:

3

Total no. in group:

4

Remarks on result:

other: Reading: 2nd reading. . Hours after challenge: 48.0. Group: test group. Dose level: 0.2%. No with. + reactions: 3.0. Total no. in groups: 4.0.

Reading:

2nd reading

Hours after challenge:

48

Group:

positive control

Dose level:

0.2%

No. with + reactions:

3

Total no. in group:

4

Remarks on result:

other: Hydroquinone was the positive control, see details under test chemical

Reading:

2nd reading

Hours after challenge:

48

Group:

test chemical

Dose level:

2%

No. with + reactions:

3

Total no. in group:

4

Remarks on result:

other: Reading: 2nd reading. . Hours after challenge: 48.0. Group: test group. Dose level: 2%. No with. + reactions: 3.0. Total no. in groups: 4.0.

Reading:

2nd reading

Hours after challenge:

48

Group:

positive control

Dose level:

2%

No. with + reactions:

3

Total no. in group:

4

Remarks on result:

other: Hydroquinone was the positive control, see details under test chemical

Reading:

2nd reading

Hours after challenge:

48

Group:

test chemical

Dose level:

20%

No. with + reactions:

4

Total no. in group:

4

Remarks on result:

other: Reading: 2nd reading. . Hours after challenge: 48.0. Group: test group. Dose level: 20%. No with. + reactions: 4.0. Total no. in groups: 4.0.

Reading:

2nd reading

Hours after challenge:

48

Group:

positive control

Dose level:

20%

No. with + reactions:

4

Total no. in group:

4

Remarks on result:

other: Hydroquinone was the positive control, see details under test chemical

Reading:

other: 3rd reading

Hours after challenge:

72

Group:

negative control

Dose level:

vehicle

No. with + reactions:

0

Total no. in group:

4

Remarks on result:

other: Reading: other: 3rd reading. . Hours after challenge: 72.0. Group: negative control. Dose level: vehicle. No with. + reactions: 0.0. Total no. in groups: 4.0.

Reading:

other: 3rd reading

Hours after challenge:

72

Group:

test chemical

Dose level:

0.2%

No. with + reactions:

2

Total no. in group:

4

Remarks on result:

other: Reading: other: 3rd reading. . Hours after challenge: 72.0. Group: test group. Dose level: 0.2%. No with. + reactions: 2.0. Total no. in groups: 4.0.

Reading:

other: 3rd reading

Hours after challenge:

72

Group:

positive control

Dose level:

0.2%

No. with + reactions:

2

Total no. in group:

4

Remarks on result:

other: Hydroquinone was the positive control, see details under test chemical

Reading:

other: 3rd reading

Hours after challenge:

72

Group:

test chemical

Dose level:

2%

No. with + reactions:

2

Total no. in group:

4

Remarks on result:

other: Reading: other: 3rd reading. . Hours after challenge: 72.0. Group: test group. Dose level: 2%. No with. + reactions: 2.0. Total no. in groups: 4.0.

Reading:

other: 3rd reading

Hours after challenge:

72

Group:

positive control

Dose level:

2%

No. with + reactions:

2

Total no. in group:

4

Remarks on result:

other: Hydroquinone was the positive control, see details under test chemical

Reading:

other: 3rd reading

Hours after challenge:

72

Group:

test chemical

Dose level:

20%

No. with + reactions:

4

Total no. in group:

4

Remarks on result:

other: Reading: other: 3rd reading. . Hours after challenge: 72.0. Group: test group. Dose level: 20%. No with. + reactions: 4.0. Total no. in groups: 4.0.

Reading:

other: 3rd reading

Hours after challenge:

72

Group:

positive control

Dose level:

20%

No. with + reactions:

4

Total no. in group:

4

Remarks on result:

other: Hydroquinone was the positive control, see details under test chemical

Interpretation of results:

Category 1B (indication of skin sensitising potential) based on GHS criteria

Conclusions:

The results showed the sensitising potential of Hydroquinone following intradermal induction at 2%, followed by an occlusive topical induction at 0.2, 2 or 20% in 80% acetone, and challenge with open applications at the same dose levels. Based on criteria described in CLP Regulation (EC) 1272/2008, the substance meets the criteria of sensitiser sub-category 1B (≥ 30 % responding at > 1 % intradermal induction dose).

Reference 2

Endpoint:

skin sensitisation: in vivo (LLNA)

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Remarks:

Comparable to guideline study with acceptable restrictions: no data on clinical signs of local irritation or systemic toxicity, on body weights or on positive controls, sufficient documentation; study acceptable as key study

Reason / purpose for cross-reference:

reference to other study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 429 (Skin Sensitisation: Local Lymph Node Assay)

Deviations:

yes

Remarks:

(no data on clinical signs of local irritation or systemic toxicity, on body weights or on positive controls)

GLP compliance:

not specified

Type of study:

mouse local lymph node assay (LLNA)

Species:

mouse

Strain:

CBA

Sex:

female

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: Harlan UK Ltd., Bicester, Oxford, UK
- Age at study initiation: 7-12 w
- Housing: standard conditions, 4 per cage
- Diet: Special Diets Services Ltd. (SDS) Porton Combined Diet (PCD) pelleted Diet (Special Diets Services Ltd., Witham, UK), ad libitum
- Water: tap water ad libitum
- Acclimation period: no data

ENVIRONMENTAL CONDITIONS:
- Temperature (°C): not specified, standard conditions
- Humidity (%): not specified, standard conditions
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): standard conditions

Vehicle:

other: acetone/olive oil (4:1) (AOO), methylethylketon (MEK), dimethyl formamide (DMF), propylene glycol (PG), dimthyl sulfoxide (DMSO), acetone/physiological saline (1:1) (APS), or acetone

Concentration:

0.05, 0.1, 0.25, 0.5, 1.0% (first test with all vehicles)
2.5, 5.0, 10% (second test with PG and APS)

No. of animals per dose:

4

Details on study design:

RANGE FINDING TESTS: no data

MAIN STUDY
ANIMAL ASSIGNMENT AND TREATMENT
- Name of test method: standard LLNA protocol
- Criteria used to consider a positive response: Stimulation index of at least 3.0

TREATMENT PREPARATION AND ADMINISTRATION:
Standard LLNA protocol (pooled animal approach):
Application of 25 µL/d on the dorsum of both ears of the test substance solution or the vehicle alone on 3 consecutive days; i.v. application of [3H]-methylthymidine on day 6 followed by sacrifice 5 hrs later and excision of draining auricular lymph nodes, which were pooled for each experimental group; Incorporation of 3H-TdR measured in cell pellets by ß-scintillation counting

EVALUATIONS:
mean disintegration per minute (dpm) per node for each group;
stimulation index = increase in dpm of HQ-treated group relative to vehicle control group;
EC3-value: linear interpolation of the dose-response data was used to calculate the estimated concentration required to induce a SI of 3

Parameter:

SI

Value:

>= 12.1 - <= 25.8

Test group / Remarks:

1.0% (Acetone/olive oil)

Remarks on result:

other: See results in other vehicles in table 1

Parameter:

SI

Value:

>= 11.2 - <= 17.2

Test group / Remarks:

0.5% (Acetone/olive oil)

Remarks on result:

other: See results in other vehicles in table 1

Parameter:

SI

Value:

>= 4.3 - <= 9.2

Test group / Remarks:

0.25% (Acetone/olive oil)

Remarks on result:

other: See results in other vehicles in table 1

Parameter:

SI

Value:

>= 1.2 - <= 2.7

Test group / Remarks:

0.1 % (Acetone/olive oil)

Remarks on result:

other: See results in other vehicles in table 1

Parameter:

SI

Value:

ca. 1.3

Test group / Remarks:

0.05% (Acetone/olive oil)

Remarks on result:

other: SI: see overview in Table 1 mean EC3 as % HQ: acetone 0.08%, MEK 0.09%, AOO 0.15%, DMF 0.21%, DMSO 0.35%, PG 1 - 2%, APS 1 - 2% mean EC3 as µg HQ/cm2: acetone 20, MEK 22.5, AOO 37.5, DMF 52.5, DMSO 87.5, PG 250 - 500, APS 250 - 500

Table 1: LLNA results as stimulation index (SI) and EC3 values of HQ in 7 different vehicles (concentration range 0.05 – 1.0%)

 

Vehicle	Laboratory	Stimulation index (SI of vehicle alone = 1.0)					EC3 (% HQ)
		0.05	0.1	0.25	0.5	1.0
AOO	1	1.3	2.7	9.2	17.2	25.8	0.11
	2	1.3	1.2	4.3	11.2	12.1	0.19
MEK	1	1.9	2.9	13.9	23.0	24.5	0.10
	2	2.2	3.6	14.0	19.8	30.9	0.08
DMF	1	0.8	1.8	3.7	7.3	8.0	0.19
	2	1.6	1.8	3.2	7.7	10.9	0.23
PG	1	0.7	0.9	1.2	1.9	2.0	> 1.0
	2	1.5	1.0	1.0	1.1	1.0	> 1.0
DMSO	1	1.1	0.9	2.6	4.0	4.2	0.33
	2	1.2	1.2	1.9	4.2	6.5	0.37
APS	1	0.7	1.0	0.9	1.9	1.9	> 1.0
	2	1.4	0.8	1.2	1.3	1.9	> 1.0
Acetone	1	1.3	5.6	13.0	15.3	24.1	0.07
	2	1.8	3.9	9.3	25.7	25.1	0.08

 

List of vehicles: acetone/olive oil (4:1) (AOO), methylethylketon (MEK), dimethyl formamide (DMF), propylene glycol (PG), dimthyl sulfoxide (DMSO), acetone/physiological saline (1:1) (APS), or acetone

 

Table 2: LLNA results as stimulation index (SI) and EC3 values of HQ in PG and APS at higher concentrations (Results from Laboratory 2)

 

Vehicle	Stimulation index (SI of vehicle alone = 1.0)			Estimated EC3 (% HQ)
	% HQ in vehicle
	2.5	5.0	10.0
PG	5.5	13.7	19.4	1 to 2
APS	6.8	10.9	11.1	1 to 2

Interpretation of results:

Category 1 (skin sensitising) based on GHS criteria

Conclusions:

HQ was found to be a sensitiser in LLNA with the different vehicles acetone/olive oil (4:1) (AOO), methylethylketon (MEK), dimethyl formamide (DMF), propylene glycol (PG), dimthyl sulfoxide (DMSO), acetone/physiological saline (1:1) (APS), or acetone. The following mean EC3 values were found: for acetone 0.08%, for MEK 0.09%, for AOO 0.15%, for DMF 0.21%, for DMSO 0.35%, for PG and APS 1 - 2%.

Executive summary:

Possible vehicle effects on the sensitising potential of hydroquinone were investigated by two laboratories in a mouse local lymph node assay comparable to standard conditions of the OECD Guideline 429. The different vehicles were acetone/olive oil (4:1) (AOO), methylethylketon (MEK), dimethyl formamide (DMF), propylene glycol (PG), dimthyl sulfoxide (DMSO), acetone/physiological saline (1:1) (APS), and acetone and the tested concentration range was 0.1 – 1.0%. PEG and APS were retested at higher concentrations ranging from 2.5 - 10% (results from one laboratory). The following mean EC3 values were found: for acetone 0.08%, for MEK 0.09%, for AOO 0.15%, for DMF 0.21%, for DMSO 0.35%, for PG and APS 1 - 2%. Calculated as µg HQ/cm² the following EC3 values resulted: for acetone 20, for MEK 22.5, for AOO 37.5, for DMF 52.5, for DMSO 87.5, for PG and APS 250 – 500 µg/cm². Consequently the sensitising potential was highly dependent on the vehicle covering a range of EC3 values from 0.08 to up to 1 – 2 %.

Reference 3

Endpoint:

skin sensitisation: in vivo (LLNA)

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Remarks:

Comparable to guideline study with acceptable restrictions: no data on clinical signs of local irritation or systemic toxicity, on body weights or on positive controls, sufficient documentation; study acceptable as key study

Reason / purpose for cross-reference:

reference to other study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 429 (Skin Sensitisation: Local Lymph Node Assay)

Deviations:

yes

Remarks:

(no data on clinical signs of local irritation or systemic toxicity, on body weights or on positive controls)

GLP compliance:

not specified

Type of study:

mouse local lymph node assay (LLNA)

Species:

mouse

Strain:

CBA

Sex:

female

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: Harlan Seralab, Bicester, Oxfordshire, UK (Laboratories A and B), Harlan sprague-Dawley, Inc., Indianapolis, IN or Jackson Laboratories, Bar Harbour, ME, USA (Laboratories C, D and E)
- Age at study initiation: 6 - 12 w
- Weight at study initiation: no data
- Housing: no data
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: no data


ENVIRONMENTAL CONDITIONS: standard, no further details

Vehicle:

acetone/olive oil (4:1 v/v)

Concentration:

0.10, 0.25, 0.50, 1.0, 2.5%

No. of animals per dose:

5

Details on study design:

RANGE FINDING TESTS: no data

MAIN STUDY
ANIMAL ASSIGNMENT AND TREATMENT
- Name of test method: standard LLNA protocol (Laboratories A and B), modified LLNA protocol 1 (Laboratories C and D), modified LLNA protocol 2 (Laboratories E)
- Criteria used to consider a positive response: Stimulation index of at least 3.0

TREATMENT PREPARATION AND ADMINISTRATION:
Standard LLNA protocol (pooled animal approach):
Application of 25 µL/d on the dorsum of both ears of the test substance solution or the vehicle alone on 3 consecutive days; i.v. application of [3H]-methylthymidine on day 6 followed by sacrifice 5 hrs later and excision of draining auricular lymph nodes, which were pooled for each experimental group; Incorporation of 3H-TdR measured in cell pellets by ß-scintillation counting

modified LLNA protocol 1 (individual animal approach):
comparable to standard protocol with the following exception: only lymph nodes of indivudual animals pooled

modified LLNA protocol 2 (individual animal approach):
comparable to modified LLNA protocol 1 with the following exception: use of [125I]iododeoxyuridine in place of 3H-TdR, incorporation of 125I-UdR measured by gamma-counter

Evaluations:
mean disintegration per minute (dpm) per node for each mouse or group;
stimulation index = increase in dpm of HQ-treated group relative to vehicle control group;
EC3-value: test concentration to elicit a stimulation index of SI = 3

Positive control substance(s):

not specified

Statistics:

Bartlett's test to examine the homogeneity of the within-chemical treatment variances; when analysis of variance revealed significant differences in parametric data, experiments were compared with vehicle controls using Dunnett's t-test, for nonparametric data use of Kruskal-Wallis test followed by Dunn's multiple comparison procedure, level of significance at P<= 0.05;
Test for dose-dependent effects by Jonckheere's test with level of significance at P<= 0.01
Comparison of stimulation indices for the 5 laboratories: analysis of covariance
Derivation of EC3-values: extrapolation from regression analyses

Parameter:

SI

Value:

>= 12.2 - <= 33.4

Test group / Remarks:

2.5%

Remarks on result:

other: See Remark

Parameter:

SI

Value:

>= 8.4 - <= 25.3

Test group / Remarks:

1.0%

Remarks on result:

other: See Remark

Parameter:

SI

Value:

>= 6 - <= 23.7

Test group / Remarks:

0.5%

Remarks on result:

other: See Remark

Parameter:

SI

Value:

>= 4.8 - <= 14.9

Test group / Remarks:

0.25%

Remarks on result:

other: see Remark

Parameter:

SI

Value:

>= 2.4 - <= 3.6

Test group / Remarks:

0.10%

Remarks on result:

other: See Remark

Remarks:

Range at different test concentrations (result from 5 laboratories: 0.10%: 2.4 - 3.6; 0.25%: 4.8 - 14.9; 0.5%: 6.0 - 23.7; 1 %: 8.4 - 25.3; 2.5%: 12.2 - 33.4 Mean EC3 value calculated based on test results from 3 laboratories with values of 0.07%, 0.08% and 0.07%: mean 0.073% or 18 µg/cm2

Parameter:

other: disintegrations per minute (DPM)

Remarks on result:

other: see Table

Table: Test results in the interlaboratory evaluation of the LLNA

Test Laboratory	Para-meter	Vehicle control	Test concentration					EC3 in %	EC3 in µg/cm^2
			0.10 %	0.25 %	0.50 %	1.00%	2.50%
A	dpm	342	973	1994	4685	5207	4489	0.07^a	17.5
	SI	-	2.8	5.8	13.7	15.2	13.1
B	dpm	347	936	2165	2259	3139	4555	0.03^ad	7.5
	SI	-	2.5	5.8	6.0	8.4	12.2
C	dpm	781 ± 133	1858 ± 184 *	5484 ± 715 *	8668 ± 885 *	12412 ± 1203 *	11747 ± 1462 *	0.08^a	20.0
	SI	-	2.4	7.0	11.1	15.9	15.0
D	dpm	257 ± 49	927 ± 215 *	1228 ± 385 *	3089 ± 753 *	3922 ± 546 *	5975 ± 631 *	0.07^b	17.5
	SI	-	3.6	4.8	12.0	15.3	23.2
E	dpm	53 ± 19	167 ± 40 *	790 ± 204 *	1256 ± 219 *	1340 ± 108 *	1769± 163 *	c
	SI	-	3.2	14.9	23.7	25.3	33.4

SI = stimulation index

^amathematically derived concentration required to induce a SI of 3

^bderived by extrapolation

^c Data set inappropriate for derivation of EC3 value by extrapolation. So these data were not considered for further evaluation

d As this EC3 value is distinctly different from the values of laboratories A, C and D, it was not considered for calculation of a mean EC3 value.

* statistically significantly different from control at P<0.05 (no statistical evaluation for Laboratories A and B)

Interpretation of results:

Category 1 (skin sensitising) based on GHS criteria

Conclusions:

A strong sensitising activity of hydroquinone was indicated in the mouse local lymph node assay in an interlaboratory evaluation with a mean EC3 value of 0.073% or 18 µg/cm2.

Executive summary:

The sensitising potential of hydroquinone was investigated in a mouse local lymph node assay comparable to standard conditions of the OECD Guideline 429 in an interlaboratory evaluation with participation of five test laboratories. Test concentrations were 0.10, 0.25, 0.50, 1.00, and 2.50% HQ in acetone/olive oil (4:1) as vehicle. A strong sensitising activity of hydroquinone was indicated by a mean EC3 value of 0.073% or 18 µg/cm²based on the most reliable test data.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (sensitising)

Additional information:

Sensitisation assays in test animals

 

The sensitising potential of hydroquinone was investigated in two mouse local lymph node assays [Reliability 2] comparable to standard conditions of the OECD Guideline 429 (Key studies: Kimber et al., 1998; Lea et al., 1999).

In an interlaboratory evaluation with participation of five test laboratories test concentrations were 0.10, 0.25, 0.50, 1.00, and 2.50% HQ in acetone/olive oil (4:1) as vehicle. A strong sensitising activity of hydroquinone was indicated by a mean EC3 value of 0.073% or 18 µg/cm²as based on the most reliable test data (Key study: Kimber et al., 1998).In the second LLNA study, possible vehicle effects on the sensitising potential of hydroquinone were investigated by two laboratories. The different vehicles were acetone/olive oil (4:1) (AOO), methylethylketon (MEK), dimethyl formamide (DMF), propylene glycol (PG), dimethyl sulfoxide (DMSO), acetone/physiological saline (1:1) (APS), and acetone and the tested concentration range was 0.1 – 1.0%. PEG and APS were retested at higher concentrations ranging from 2.5 - 10% (results from one laboratory). The following mean EC3 values were found: for acetone 0.08%, for MEK 0.09%, for AOO 0.15%, for DMF 0.21%, for DMSO 0.35%, for PG and APS 1 - 2%. Calculated as µg HQ/cm² the following EC3 values resulted: for acetone 20, for MEK 22.5, for AOO 37.5, for DMF 52.5, for DMSO 87.5, for PG and APS 250 – 500 µg/cm². Consequently the sensitising potential was highly dependent on the vehicle covering a range of EC3 values from 0.08 to up to 1 – 2 % (Key study: Lea et al., 1999). Based on both key studies, the EC3 value of 0.07% or 18 µg/cm² is considered to be the NOAEL for skin sensitisation. Based on criteria of CLP, the skin sensitisation potency of HQ would be classified as extreme, sensitiser sub-category 1A, under CLP criteria [due to EC3 < 2%].

Further, the sensitising potential of hydroquinone was investigated in a guinea pig maximization test comparable to standard conditions of the OECD Guideline 406. Intradermal induction was performed with a test concentration of 2% followed by a 48-hour occlusive patch with 10% hydroquinone seven days later. After a 14-day interval, challenge was performed by application of an occlusive chamber with 5% hydroquinone to a prepared flank for 24 hrs. A positive skin reaction was observed in seven of the 10 guinea pig maximization test, giving a sensitisation rate of 70% (Key study: Goodwin et al., 1981). Because more than 30% of the animals responded at > 1% injection dose, the results correspond to sub-category 1B, strong sensitiser. Similar results were obtained in another maximisation assay, using an intradermal injection at 2%, topical induction at concentrations of 0.2, 2.0 or 20% hydroquinone on day 7, before an open application challenge with the same concentrations.

The results are relatively consistent with prior publications using the M&K assay (reported in RSS-overview). Based on the doses and % responses reported, the 3 studies would also correspond to a sub-category 1B, as the injection concentration was always > 1% with responses in > 30% of the animals

 

Overview of available study results

Test type	Species	Result	Conclusion	Test doses		Reference
Key studies
LLNA	Mouse	Positive	Sensitiser, EC3=0.073%		0.1, 0.25, 0.50, 1.0, 2.5% in acetone/olive oil (4:1)	Kimber et al., 1998
LLNA	mouse	Positive	Sensitiser, EC3=0.08% to 1-2%		1^sttest: 0.05, 0.1, 0.25, 0.50, 1.0% in various vehicles 2^ndtest 2.5, 5.0, 10%	Lea et al., 1999
GPMT	Guinea pig	Positive	Sensitisation rate 70%		Induction: 2% inj, 10% topical Challenge: 5%	Goodwin et al., 1981
GPMT	Guinea pig	Positive	Sensitisation rate 75% to 100%		Induction: 2% inj, 0.2%, 2% or 20% topical (in 80% acetone) Challenge: 0.2%, 2% or 20% (in 80% acetone), open application	To-o et al., 2010
Supporting studies
GPMT	Guinea pig	Positive	Sensitisation rate 50%, grading 3^a	0.5M inj- 1M ind., (i.e. 5 and 10%)		Van der Walle et al., 1982
GPMT	Guinea pig	Positive	Strong sensitizer	Induction: 2% inj, 1% topical Challenge: 0.5%. Response: Strong, 65-80% incidence (M&K, 1969)		Basketter and Goodwin, 1988
GPMT	Guinea pig	Positive	Sensitisation rate 100%	Induction: 2% inj, 1% topical Challenge: 0.5%.		Basketter and Scholes, 1992
^a according to Magnusson and Kligman

 

 

The sensitising potential of hydroquinone indicated in the key studies is supported by further positive test results in the Local Lymph Node Assay (LLNA) (Basketter and Scholes, 1992; Kimber et al., 1994), in the Guinea Pig Maximization Test according to Magnusson and Kligman (Van der Walle et al., 1982; Basketter and Goodwin, 1988; Basketter and Scholes, 1992), in the Freund’s Complete Adjuvant Test (FCAT) (Van der Walle et al., 1982), in the Cumulative Contact Enhancement Test (CCET) (Basketter and Goodwin, 1988), the Single Injection Adjuvant Test (SIAT) and the modified Draize test (Goodwin et al., 1981) (all supporting data compiled without detailed evaluation).

 

Human Experience

Human experience on a possible sensitising effect of HQ can be evaluated in a weight of evidence approach.

 

Several publications report on patch tests performed according to standardized conditions, generally with 48 h application via Finn chambers and reading according to ICDRG criteria after 48 and 72 h, and 4 to 6 days. There was no indication of sensitisation to HQ in patch tests with patients of Finnish dermatology clinics (populations partly overlapping covering a total study period of 1985 to 1996: Tarvainen et al. 1995; Kanerva et al. 1997, 1999), or a group of 54 Finnish hairdressers with work-related skin and respiratory symptoms (Leino et al. 1998). From 65 persons working at a film laboratory (number with exposure to HQ not known) 4 (6.2%) showed a positive patch test reaction to 1% HQ. The vehicle was found to influence the outcome of findings. Whereas no skin reaction was observed with 1% HQ in petrolatum, 1% HQ in water provoked erythema (irritant reaction) and staining possibly due to instability of HQ in aqueous solution (Liden 1989).

After a skin bleaching procedure with a 7-day treatment with a skin bleaching cream (5% HQ, 10% glycolic acid) a 47-year old woman developed an allergic contact dermatitis. Patch test reactions were positive both to the bleaching cream (++) and to 1% HQ (+). In the observed case, presumably an increased skin permeation of HQ existed due to a cosmetic keratolytic pretreatment of the skin, which could have favoured sensitisation (Barrientos et al., 2001).

 

Overall, despite a long history of use, observations of exposure-related skin sensitisation in humans are not frequent. The literature data on human clinical studies (human patch tests for diagnosis purpose, usually conducted with 1% HQ as part of a standard allergen series) or case reports have been reviewed in section 7.10.4 of the IUCLID, and indicate that hydroquinone is not a significant skin contact allergen in humans. Additional sources (German publications) have been also discussed by the MAK commission (The MAK Collection for Occupational Health and Safety, Volume 10, 1994, http://onlinelibrary.wiley.com/doi/10.1002/3527600418.mb12331e0010/pdf).

 

The positive levels in patch tests were usually observed at 1% or higher, and were dependent on vehicle used. Irritation reactions were also observed when HQ was applied in water.

The prevalence in professional users (in particular hair-dressers) has been reported in the past to be below 1%.

Other adverse skin effects (ochronosis, irritation) have been associated with high concentrations or overuse, especially in medicinal uses.

Short description of key information:
Local lymph node assay (comparable to OECD Guideline 429): mean EC3 0.07% or 18 µg/cm2 (Kimber et al., 1988); the sensitising potential was highly dependent on the vehicle covering a range of EC3 values from 0.08 to up to 1 – 2 % (Lea et al., 1999)
Guinea pig maximization test (comparable to OECD Guideline 406): sensitization rate 70% following intradermal injection at 2%. In another study, similar to OECD 406, with reduced animal numbers, incidence was 75 to 100% depending on the concentration at challenge after an intradermal induction concentration of 2%
Human data (patch tests for diagnosis purpose, case reports, history of use) indicate a low frequency of exposure-related sensitization cases despite a long history of use.
By weight of evidence considering the experimental data in animals, clinical studies in humans and history of use, the substance is considered a skin sensitiser sub-category 1B (see discussion).

Justification for selection of skin sensitisation endpoint:
Positive effects observed in various animals studies and case reports in humans indicate a sensitisation potential. By weight of evidence considering the experimental data in animals, clinical studies in humans and history of use, the substance is considered to be a skin sensitiser sub-category 1B.

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

The experimental results in the mice LLNA and in the guinea-pig M&K indicate a clear sensitizing potential, however the potency seems to differ between both test methods. The LLNA model assesses the ability of the substance to simulate the lymphocyte proliferative response during the induction phase, while the Maximisation test assessed both the induction and the elicitation phases, and may be more reliable in assessing the sensitisation potency of Hydroquinone.

Furthermore the human data (mainly diagnostic patch test data) tend to support that hydroquinone is not a significant human skin sensitizer.

Results in humans and Maximisation assay support classification in sub-category 1B.

According to the criteria of EC directive 1272/2008 and GHS, Hydroquinone is classified as Skin Sensitiser Sub-Category 1B; H317: May cause an allergic skin reaction, based on a weight of evidence.