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Skin irritation:
9-octadecenoic acid caused no irritations on intact skin, but led to irritations on scarified skin in the concentrations tested.
Cholecystokinin release was increased after intake of 9-octadecenoic acid, but no indications for carcinogenic properties were found.

Additional information

Direct observations in humans

Skin irritation

In a publication another test method for skin irritation using a so called “Duhring Chamber” is described. In this publication there are also test results with 9-octadecenoic acid (CAS 112 -80 -1) applied to the skin of humans given. This substance was tested in 2 concentrations, 5 and 25 % in ethanol. 0.1 mL of each concentration was pipetted onto a disc of non-woven cotton cloth fitting the Duhring Chamber, which was then fixed to the skin by sealing with non-occlusive tape. As a result, the irritant responses were found to be dose dependent: The read across substance caused moderate irritations to the scarified skin at a concentration of 5 % and marked irritation at a concentration of 25 %. It has to be kept in mind that the skin was scarified before application of the read across substance, which probably increased the irritation effect. In the publication it is indicated that the threshold concentration for the read across substance is 30 % on normal skin compared to 5 % on scarified skin.  

In another publication an experiment is described in which several substances (surfactants, including 9-octadecenoic acid) were tested for their skin irritation potential. The test was conducted on humans. The substances were applied to healthy skin and to skin exhibiting pre-existing dermatitis for the purpose of comparison. The following test groups were treated: group 1: 40 healthy subjects (10 men and 30 women) group 2: 19 mean and 21 women with atopic dermatitis group 3: 26 men and 31 women with active psoriasis group 4: 31 men and 93 women with eczema, giving positive patch test responses group 5: 53 men and 87 women with eczema with no patch test responses group 6: 21 men and 58 women with active urticaria group 7: 14 men and 26 women with generalized pruritus. As positive controls, 15 µL aqeuous solution of one of the known irritants benzalkonium chloride (BAK) 1 %, sodium lauryl sulphate (SLS) 1 % and dimethylsulfoxide (DMSO) 10 % were applied to one of two test sites on the upper back. The analogue substance was applied to the other test site in a concentration of 5 % as an aqueous solution under a semi-occlusive dressing. The exposure time was 2 days except for additionally patches that were applied to patients with urticaria, these were removed after 30 min. After 2 days of exposure with the analogue substance, positive responses were found in 0.2 % of the test persons. Exposure with the positive controls led to positive reactions in 36 % (BAK), 38 % (SLS) and 1.3 % (DMSO) persons, respectively. Positive responses to both BAK and SLS were seen in 22 %. As a conclusion, the number of positive skin reactions to the analogue substance was low in all test groups. It was concluded in the publication that the tested substance is not irritating to the skin.


In a publication (Beardshall, K. 1989), a study is described in which the effect of oral intake of the read across substance (9-octadecenoic acid) on cholecystokinin (CKK) release in humans was examined. The study was conducted on 5 man and 1 woman who drank 3.5 g of the read across substance administered with 10 mL Hycal and 150 mL water after fasting overnight. The procedure was repeated after at least one week. Blood was sampled before intake and several times after consumption of the substance to measure the CKK concentration and other regulatory peptides. As a result, an increase in CKK release was observed, reaching in the highest concentration of cholecystokinin 30 min after intake of the read across substance. The neurotensin concentration in the blood was not increased. CKK promotes pancreatic growth and neoplasia in rats (as noted in this publication). But on the basis of this short-term study no link can be drawn between pancreatic cancer and an increase in CKK release.