Repeated Application Test Research Articles

Effects of different base agents on prediction of skin irritation by sodium lauryl sulfate using patch testing and repeated application test

Animal testing for cosmetics was banned in the European Union (EU) in 2013; therefore, human tests to predict and ensure skin safety such as the patch test or usage test are now in demand in Japan as well as in the EU. In order to investigate the effects of different bases on the findings of tests to predict skin irritation, we performed patch testing (PT) and the repeated application test (RAT) using sodium lauryl sulfate (SLS), a well-known irritant, dissolved in 6 different base agents to examine the effects of these bases on skin irritation by SLS. The bases for PT were distilled water, 50% ethanol, 100% ethanol, a gel containing 50% ethanol, white petrolatum, and hydrophilic cream. The concentrations of SLS were 0.2% and 0.5%. Twelve different base combinations were applied to the normal back skin of 19 individuals for 24h. RAT was performed with distilled water, 50% ethanol, 100% ethanol, a gel containing 50% ethanol, white petrolatum, and hydrophilic cream containing SLS at concentrations of 0.2%, 2%, and 5%, being applied to the arms of the same PT subjects. The test preparation of each base was applied at the same site, with 0.2% SLS being used in the first week, 2% SLS in the following week, and 5% SLS in the final week. The results of PT revealed that skin irritation scores varied when SLS at the same concentration was dissolved in a different base. The results of RAT showed that although skin irritation appeared with every base at a concentration of 5%, the positive rate was approximately the same. In conclusion, our results suggest that skin irritation elicited in PT depends on the base, while in RAT, it does not depend on the type of base employed.

A study of skin responses to follow-up, rechallenge and combined effects of irritants using non-invasive measurements

Irritant contact dermatitis is a common clinical problem. Primary irritation can be easily recognized, but cumulative irritation by daily exposure is hard to be diagnosed and the condition may fail to be clear even away from work. The mechanism of irritant dermatitis produced by repeated or combined exposure to clinical or subclinical doses of irritants is still poorly understood. In order to find out whether the subclinical doses of irritants affect each other by repeated or combined exposure according to their concentrations, non-invasive measurements, transepidermal water loss and laser Doppler flowmetry were used. Sodium lauryl sulfate, sodium hydroxide and benzalkonium chloride were serially diluted and patch-tested with large Finn chambers on Scanpor tape on the back of normal human volunteers and responses were followed up for 7 days. Twice repeated exposure with subclinical doses of irritants at 1 day intervals were also performed. Repeated daily applications for 5 days with subclinical doses of single or premixed irritants were performed to know the combined irritating effect. The irritant response was well correlated to the concentration of the irritants. However, increased response was not observed when subclinical doses were rechallenged on the previously patch tested sites. Twice-repeated exposure of subclinical doses of irritants increased skin irritancy when measured by transepidermal water loss and laser Doppler flowmetry. Some correlation and some discrepancies were observed between different evaluation methods in combined and repeated application tests with irritants of subclinical doses. Responses of skin irritancy induced by subclinical doses showed somewhat different pattern from that given strong irritants. So, when evaluating the patients suspicious of irritant dermatitis, patch testing with the possible combination of the irritants or repeated test may be helpful to verify their effect on the skin even at a weak concentration.

Safety evaluation of gums and thickeners used in cosmetic formulations

Synopsis Safety tests have been carried out on gums and thickeners, continuing a study involving commonly used cosmetic ingredients (1, 2, 3, 4). The ocular and cutaneous tolerance tests have been conducted on the rabbit following the official French methods (5, 6) but with some complements or modifications (1, 2, 3, 4, 7). The test substances (listed in Table 1) were products from various suppliers and of different types and grades. None of the fifty samples tested provoked pathological lesions of the ocular mucous membrane; nevertheless, corneal irritation was noted with silicates, silica and bentonite, probably due to mechanical effect, when applied at relatively high concentration. The highest score on the primary cutaneous irritancy test (moderately irritant) was that for the gelled volatile hydrocarbon solvents. The repeated application test was continued for 6 weeks: no significant pathological reaction was observed. Only a slight intolerance was noted with the gels of volatile hydrocarbons and isopropyl myristate, but the irritant reactions were significantly reduced compared to those previously observed with the pure oils (1, 2). Consequently, based on these data, it can be concluded that the use of gums and thickeners involved in this publication presents no hazard for the skin.

Etude de tolérances oculaire et cutanée chez le lapin, de différentes matières premières utilisées en cosmétologie, et provenant de fabrications diverses (2ème partie)

Summary Different lots of a number of oils used in cosmetics were subjected to different storage times, analysed and their effects on rabbit eye and skin were assessed following the official French methods. The scoring system diverged slightly from the official method and was described in Part I (1). All products were tested pure in the eye test without rinsing and no corneal involvement was found. Slight congestion of the iris and conjuctivae was noted. The products showing the worst (slightly irritant) score were one sample each of avocado oil and ethyl esters of turtle oil. The highest score on the primary cutaneous irritancy test (slightly irritant) was that for the volatile hydrocarbon solvents which also gave an oedematous reaction. On dilution or on open test the reactions were negligible. The repeated application test was continued only for 8 weeks (instead of 90 days) and a histological examination was carried out on treated areas at the end of this period. The oils were applied pure and in aqueous emulsion - 10% or 2% where a severe reaction was observed. Of five samples of sweet-almond oil one showed a high degree of oxidation (peroxide value 35 meq kg(-1)). This sample did not give any significant adverse reaction whereas some irritation and vesicularisation was obtained with a sample of low peroxide value stored under nitrogen. Two of the four samples of avocado oils tested showed severe irritation and vesicle formation after 6 weeks application of the pure oil although no analytical differences were found to correlate with this result. A commercial sample of the unsaponifiable fraction of avocado oil (prepared by molecular distillation) showed severe reactions in the three rabbits treated with the pure oil, the study being terminated after 5 weeks.