204 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS ].4 _• 0.6 - •: 0.4 - •' 0.2 - 8 I0 ALKYL CHAIN LENGTH alkyl $uloeat½$ (5). Putterman eta/. (3) compared skin swelling as a result of treatment with SLS, AEOS-1EO, and AEOS-3EO and showed that ethoxylation produced decreases in the swelling response. Rhein eta/. (10) compared the swelling induced in stratum corneum by AEOS containing 0, 1, 2, 3, 6, and 12 moles of EO, and found that swelling decreased with increased ethoxylation up to 6 ethylene oxide units, after which no further decreases in swelling could be detected. Table II compares in vivo human skin irritation scores and collagen swelling as a func- tion of EO content in AEOS surfactants. Human skin irritation was determined in vivo by the method of Frosch and Kligman (11). The treatments were applied to subjects with Duhring chambers for 5 days. The most severe irritation and highest collagen swelling was produced by the unethoxylated parent ALS (AEOS-0EO), and the severity of irritation and swelling decreased with ethoxylation of alkyl sulfate. No significant difference was found between the swelling produced by AEOS-9EO and water, and no irritation was found after 5 days of treatment. The effect of variation in the EO content of AEOS on irritation potential was also studied by Opdyke and Burnett (12). These workers used the Guinea Pig Immersion procedure to evaluate ammonium lauryl sulfates with 0, 1, 3, and 7 moles of ethylene oxide. AEOS-0EO (ALS) was toxic to all treatment animals, and AEOS-7EO was the mildest. The data clearly show that increasing the ethylene oxide content in AEOS surfactants produced corresponding decreases in human (Table III) and animal (12) skin irritation, in agreement with the results of the collagen swelling assay (Table III).

COLLAGEN SWELLING PREDICTS SURFACTANT IRRITATION 205 10 o• AEO o i o u AEO • o o AEOS-6 o • AEOS-9 o o o o o H2 0 0 I I I I I 0 2 4 6 8 I0 SURFACTANT CONCENTRATION (mMOLAR) Figure 4. Effect of ethoxylation of C12 alkyl sulfates on collagen swelling. EFFECT OF SURFACTANT CHARGE ON COLLAGEN SWELLING The effect of surfactant charge on collagen swelling was studied by treating collagen film with 10 mM solutions of anionic, nonionic, amphoteric, and cationic surfactants. Table III shows that the substrate responded by swelling to the treatment by anionic Table II Effect of Ethoxylation of C12 Alkyl Ether Sulfate on Skin Irritation and Collagen Swelling Skin Irritation Collagen Swelling (ml/g) Surfactant (In Vivo) (+) (In Vitro) (+ +) AEOS-0EO (ALS) Severe within 1 day 8.9 -+ 0.2 (a) AEOS-3EO Mild to moderate by 5th day 4.2 _+ 0.1 (b) AEOS-6EO Mild to moderate by 5th day 3.5 -+ 0.1 (c) AEOS-9EO None after 5 days 2.7 _+ 0.1 (d) Water -- 2.2 _+ 0. i (d) +, Irritation in vivo.' Human subjects, 10% concentration, pH 7, 2 to 3 subjects, Duhring chambers, 5 days. -F +, Collagen swelling test conditions: 2 replicates, concentration 10 mM, time 24 hours, pH 7.0. Values which are significantly different have different symbols (a, b, c, d) (p 0.05).