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Toxicological information

Endpoint summary

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Administrative data

Description of key information

No skin sensitisation study with substance Fatty acids, C18-24, zinc salts is available, thus the skin sensitisation potential will be addressed with existing data on the individual moieties zinc and fatty acids, C18-24. Substance Fatty acids, C18-24, zinc salts is not expected to show signs of dermal sensitisation, since the two moieties zinc and fatty acids, C18-24 have not shown any skin sensitisation potential in experimental studies, respectively long-term experience has shown that they lack such a potential.

Key value for chemical safety assessment

Skin sensitisation

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


Substance Fatty acids, C18-24, zinc salts  is not expected to show signs of dermal sensitisation, since the two moieties zinc and fatty acids, C18-24 do not have a skin sensitisation potential in experimental studies respectively in long experience of dermal use.

Thus, substance Fatty acids, C18-24, zinc salts 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.

This conclusion is in line with the conclusion of an EU risk assessment carried out on the structural analogue substance Fatty acids, C16-18, zinc salts (i.e. zinc stearate) within the framework of EU Existing Chemicals Regulation 793/93 (EU RAR Zinc stearate (CAS# 91051-01-3, CAS# 557-05-1) Part IIHuman Health. EUR 21168 EN ( Animal data on skin sensitisation are not available for zinc distearate. However, based on the accepted derogation and the fact that zinc oxide is not a skin sensitiser, it is consequently concluded that zinc distearate is not likely to be skin sensitising, and therefore does not need to be classified/labelled. This is supported by the fact that the use of zinc distearate in pharmaceutical and cosmetic products is without reported skin sensitisation effects.

Please refer to the section for the respective assessment entity for data on the moieties. In brief:


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.


Fatty acids are generally not considered to represent a risk to humans, which is reflected in their exclusion from REACH registration requirements (c.f. REACH Annex V (Regulation (EC) No 987/2008)).

The linear, saturated, even numbered C18-24 fatty acids are present in in breast milk, body fat and skin lipids and in natural fats from vegetal as well as animal origin used as human and animal nutrients, in skin cosmetics and pharmaceuticals or for technical applications (Alvarez and Rodriguez 2000, Gunstone 2004, Kingsbury et al. 1961, Krist et al. 2008, Mojumdar et al 2015, Much et al. 2013, Yuhas et al. 2006). Based on this, the following endpoint is covered by publically available data on fatty acids with the same or similar structure.

Fatty acids, fatty acids salts and natural oils from which the fatty acids are derived have a long history of use in products intended for dermal application. A lack of a sensitisizing potential can be taken as granted from experience of safe use of those products (HERA 2002, CIR, 1982, 1987, European Pharmacopoeia 8.0), and was also experimentally confirmed e.g. by animal and human skin sensitisation tests of respective cosmetic formulations (CIR, 1987) or as negative control in skin sensitation tests when they have been used as formulating agent (Schlede and Eppler 1995).

Respiratory sensitisation

Endpoint conclusion
Endpoint conclusion:
no study available

Justification for classification or non-classification

As the two moieties of substance Fatty acids, C18-24, zinc salts are not sensitising, substance Fatty acids, C18-24, zinc salts in all probability has also no sensitising activity.

According to the criteria of REGULATION (EC) No 1272/2008 and its subsequent adaptions, substance Fatty acids, C18-24, zinc salts does not have to be classified and has no obligatory labelling requirement for sensitization by skin contact.

Substance Fatty acids, C18-24, zinc salts is not classified for respiratory sensitisation because of lack of data.