38 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

SKIN IRRITATION POTENTIAL OF SURFACTANTS 39 many others for the study of specific histamine-releasing agents (14), and full details are to be published elsewhere (15). There was always a very low level of spontaneous histamine release from the mast cells on incubation (generally less than 10•o) in the absence of surfactants. However, as the concentration of surfactant was increased, a level was reached when there was rapid release of the stored histamine (up to 85•o of the total). Further increase in the concentration of surfactant did not release more. The relationship between a series of surfactants, all with a 12-carbon lipophilic chain, but with a variety of polar headgroups, and histamine-releasing potential is shown in Table VI. Sodium lauryl Table VI. The ability of 12-carbon chain length surfactants of various polar head groups to release histamine from rat mast cells in vitro Surfactant Concentration Critical micelle (mM) at which concentration in histamine was buffer at 22 ø released (mM) Lauryl alcohol No effect at 1 m•a Water insoluble Lauryl monoethoxylate 0.2-0.5 0.1 Lauryl triethoxylate 0.03 0.03 Lauryl hexaethoxylate 0.02-0.05 0.035 Sodium lauryl sulphate 0.03 1.0 Sodium lauryl mono- ethoxy sulphate 0.05 0.15 Sodium lauryl tri- ethoxy sulphate 0.05 0.2 Sodium laurate 0.4 10.0 Sodium lauroyl isethionate 0.15 1.2 sulphate and its mono- and triethoxy derivatives were the most potent anionic surfactants, and lauryl tri- and hexaethoxylates (non-ionic surfac- tants) were equally as effective at similar concentrations. However, sodium laurate and sodium lauroyl isethionate were far less potent by almost an order of magnitude. For the anionic surfactants the concentrations to cause mast cell degranulation (i.e. histamine release) were consistently below the critical micelle concentration (CMC). The effect of chain lengths of different surfactants upon histamine release was studied and shown in Table VII. Of the anionic surfactants the series of alkyl soaps, alkoyl isethionates, alkyl sulphates and ether sulphates