Lauric acid

Endpoint summary

Description of key information

Irritation / corrosion:
- skin: not irritating (OECD 404)
- eyes: irreversible effects (OECD 405)

Key value for chemical safety assessment

Skin irritation / corrosion

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not irritating)

Eye irritation

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (irritating)

Additional information

Skin

Skin irritation was analyzed in a study performed under GLP according to OECD guideline 404, where 3 New Zealand White rabbits received an application of 0.5 g lauric acid to the shaved skin for 4 hours under semi-occlusive conditions (Daamen, 1989). The resulting mean scores for erythema and edema after 24 to 72 hours were 0.4 and 0, respectively. Thus, lauric acid was found to be not irritating to the skin.

In another study performed in accordance with OECD guideline 404, 4 “Kleinrussen” rabbits received an application of 0.5 g lauric acid to the shaved skin for 4 hours under occlusive conditions (Kästner, 1988). The resulting mean scores for erythema and edema after 24 to 72 hours were 3.1 and 2, respectively. The observed erythema and edema disappeared within 10 days, while scaling was observed until day 17 after the application. Based on the result, the study found lauric acid to be irritating to skin. However, since lauric acid was applied under occlusive condition, the result could not be taken into account for assessment.

In addition to the in vivo studies, an in vitro skin corrosivity test with lauric acid is available, which was conducted under GLP according to a method described by Oliver, Pemberton & Rhodes (1986 & 1988). Freshly clipped skin of Wistar rats was sealed to tubes and suspended to physiological solution (Whittle, 1994). 150 µL of lauric acid was the applied to the epidermal surface for 24 hours. After the exposure the test substance was removed and any deterioration in the skin was assessed by measuring the transcutaneous electrical resistance. As a result, a mean resistance of 154 +/- 1.6 kOhm/skin disc was measured indicating that lauric acid did not display properties characteristic of those substances which may be corrosive to animal skin in vivo.

In addition to studies with animals two studies with human volunteers were available for assessment (Matthies, 1988). In the first study, 10µL lauric acid at concentration of 50 % was applied to the back of 20 subjects for 24 hours using a Large Finn Chamber on Scanpor (Herma). The reactions were evaluated 1, 6, 24, 48, 72 and 14 hours later. Although erythema, edema and scaling were reported, no single score of these reactions were provided. In the second study with volunteers, lauric acid at 80% was applied to the forearm of 10 volunteers, which was repeated every 30 seconds for 30 minutes (Matthies, 1988). The reactions were scored 1 and 24 hours after the last application until disappearance of the symptoms. As result, 3/10 subjects showed erythema with the lowest score after 30 min, which disappeared after 30-35 min. The other subjects did not show any symptoms.

Together the results of the human studies show, that lauric acid can act as an irritant to skin when applied under occlusive condition. However, under open conditions, no clear irritating properties were demonstrated. In conclusion, lauric acid can be regarded as not irritating to skin taking into account the data of studies with human and animal data obtained in tests performed according to OECD guidelines.

Eye

Eye irritation was evaluated in a study performed under GLP according to OECD guideline 405, where 52.45 +/- 0.45 mg of lauric acid was instilled into the eyes of 3 New Zealand White rabbits (Daamen, 1989). The result mean scores for corneal opacity, iris, and conjunctival erythema and chemosis after 24 – 72 h were 0.9, 0.8, 2.9 and 1.6, respectively. While the effect on the iris and the edema disappeared within 7 and 21 days, respectively, corneal opacity and erythema were still present at the end of the 21 day observation period. In addition, neovacularisation starting from day 7 until day 21 was found. Thus, lauric acid was found to cause serious damage to eyes.

The same result was found in another study conducted according to OECD guideline 405, where only one “Kleinrussen” rabbit was used (Kästner, 1988). As a result of the instillation of lauric acid, the mean scores for corneal opacity, iris, and conjunctival erythema and chemosis after 24 – 72 h were found to be 1, 0.3, 0.7, and 1, respectively. However, corneal opacity was still present at the end of the 21 day observation period indicating the irritating properties of lauric acid.

Lauric acid was found to be irritating to eyes in the study perfomed according to national guidelines since corneal opacity and moderate conjunctivitis were noted which did not subside within 72 hours (Briggs, 1976).

In addition, a study with the analogue fatty acids C12-14 is used for the hazard assessment, since lauric acid is a main constituent of fatty acids C12-14 and both substances belong to the same category due to similar structural and toxicological properties. Thus, a read-across is performed based on a category approach (for details refer to IUCLID chapter 13).

Fatty acids C12-14 containing 70% lauric acid was found to be not irritating to eyes, when it was tested in a study performed according to GLP and OECD guideline 405 where 0.1 g was instilled into the eyes of three New Zealand White rabbits (Stelter, 2010). While neither mortality nor significant clinical signs of toxicity were observed until 21 days after the test item application, the resulting mean scores (24 – 48 – 72 hours) for corneal opacity, iris, conjunctival erythema and chemosis were 0, 0, 0.78, and 0.67, respectively. Thus, lauric acid at a concentration of 70% was not found to be irritation to eyes.

Effects on eye irritation: irritating

Justification for classification or non-classification

According to DSD (67/548/EEC) or CLP (1272/2008/EC) classification criteria for irritation/corrosion, lauric acid has to be classified as irritant to eye (R41; Eye Cat. 1) at concentration higher than and including 70%. Thus, SCL of 70% for R41 and eye damage Cat.1 is assigned to this substance.

No classification for skin irritation is required since the criteria for classification is not fullfiled and thus a non-classification is warranted.