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Description of key information

No skin sensitisation study with zinc didocosanoate is available, thus the skin sensitisation potential will be addressed with existing data on the individual moieties zinc and docosanoate. Zinc didocosanoate is not expected to show signs of dermal sensitisation, since the two moieties zinc and docosanoate have not shown any skin sensitisation potential in experimental studies.

Key value for chemical safety assessment

Skin sensitisation

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

zinc didocosanoate

Zinc didocosanoate is not expected to show signs of dermal sensitisation, since the two moieties zinc and docosanoate have not shown any skin sensitisation potential in experimental studies. Thus, zinc didocosanoate is not to be classified according to regulation (EC) 1272/2008 as skin sensitising. Further testing is not required. For further information on the toxicity of the individual assessment entities, please refer to the relevant sections in the IUCLID and CSR.



The skin sensitising potential of zinc oxide (purity 99.69%) was investigated in female Dunkin Hartley guinea pigs in two well-performed maximisation tests, conducted according to Directive 96/54/EC B.6 and OECD guideline 406. Based on the results of a preliminary study, in the main studies experimental animals (10 in each test) were intradermally injected with a 20% concentration and epidermally exposed to a 50% concentration (i. e. the highest practically feasible concentration). Control animals (5 in each test) were similarly treated, but with vehicle (water) alone. Approximately 24 hours before the epidermal induction exposure all animals were treated with 10% SDS. Two weeks after the epidermal application all animals were challenged with a 50% test substance concentration and the vehicle. In the first study, in response to the 50% test substance concentration skin reactions of grade 1 were observed in 4/10 experimental animals 24 hours after the challenge (40% sensitisation rate), while no skin reactions were evident in the controls. In contrast, in the second study no skin reactions were evident in the experimental animals (0% sensitisation rate), while a skin reaction grade 1 was seen in one control animal. The skin reaction observed in one control animal is probably a sign of non specific irritation (Van Huygevoort, 1999b1, 1999b2).

In a third well-performed maximisation test, conducted according to the same guidelines and with the same experimental design, another analytical grade zinc oxide was tested (Zincweiß Pharma A; purity 99.9%). The only difference with the studies described above was the intradermal induction concentration, which was 2% as for Zincweiß Pharma A this was considered the highest concentration that could reproducibly be injected. In this test no skin reactions were evident in both experimental and control animals, hence a 0% sensitisation rate for Zincweiß Pharma A. White staining of the treated skin by the test substance was observed in some animals 24 and 48 hours after challenge (Van Huygevoort, 1999a).

Human data:

In a human patch test performed with 100 selected leg-ulcer patients, 11/100 patients gave an allergic reaction with zinc ointment (60% ZnO and 40% sesame oil). However, 14/81 patients gave a positive response when treated with sesame oil alone. This study does not give any indication for a skin sensitizing potential of zinc oxide in humans (Malten and Kuiper, 1974).

The effect of zinc oxide on contact allergy to colophony was investigated. With 14 patients with earlier history of moderate patch test reactions to colophony (a patch test) with 10% ZnO (2.3 mg Zinc/cm²) with and without colophony was performed. No positive response was observed in the 14 patients when only a 10% solution of zinc oxide was used. The addition of zinc oxide to colophony decreased the allergic reaction induced by colophony (Söderberg et al., 1990). All available data suggests this compound does not have skin sensitisation potential.


docosanoic acid

Since the dermal absorption of fatty acids decreases with increasing chain length and molecular weight, the irritating and sensitising capacity of long chain fatty acids is low (Clayton & Clayton, 1982; Madsen et al., 2001). The longer chain lengths, C14 and above, are not irritant (CIR, 1987; Madsen et al. 2001). Also, the existence of unsaturated carbon chains and carbon chain lengths of C16 to C18 contribute to a low skin irritation effect (Madsen et al., 2001)” (HERA, 2002).

The non-sensitising properties of long chain fatty acids were demonstrated in “a skin sensitisation study in 28 volunteers. Five 48-hour covered applications of 1% decanoic acid (C10) in petrolatum were made over a 10 day period. The results were negative since none gave positive reactions when challenged 10-14 days after the induction phase with a final 48-hour closed patch test using 1% in petrolatum (IUCLID, 2000a)” (HERA, 2002).

Further on, “no local reactions indicative of sensitisation were seen in 100 subjects patch tested [under unspecified conditions] with a bath soap and detergent formulation containing 0.3-0.75% sodium stearate (BIBRA, 1990). De Groot et al. (1988) reported that 25 subjects showed no sensitisation reactions when exposed to 5% stearic acid (C18) in petrolatum and a 1% aqueous sodium stearate solution” (HERA, 2002).

“Two eye shadow formulations, each containing 10% zinc distearate were tested by means of the Schwartz-Peck Prophetic Patch Test (202 volunteers) and the Draize-Shelanski Repeated Insult Patch Test (99 volunteers). Both tests resulted in “virtually 0 reactions”. One of the formulations was applied twice daily for 28 days to 52 females. No “irritation or sensitisation” was noted when examined up to four weeks after application (CIR, 1982)” (EU Risk Assessment report- Zinc distearate, 2004).


Sensitisation by or intolerance to an abundantly available essential substance such as docosanoic acid would be grossly implausible and can therefore safely be excluded.

Respiratory sensitisation

Endpoint conclusion
Endpoint conclusion:
no study available

Justification for classification or non-classification

As the two moieties of zinc didocosanoate are not sensitising, zinc didocosanoate in all probability has also no sensitising activity.

According to the criteria of REGULATION (EC) No 1272/2008 and its subsequent adaptions, zinc didocosanoate does not have to be classified and has no obligatory labelling requirement for sensitization by skin contact.

Zinc didocosanoate is not classified for respiratory sensitisation because of lack of data.