Water-resistant sunscreen-preparation 649 4 Owens, D. W., Knox, J. M., Hudson, H. T. and Troll, D. Influence of humidity on ultraviolet injury. J. Invest. Dermatol. 64 250 (1974). 5 Harris, D. R., Polk, F. and Willis, I. Evaluating sweat gland activity with imprint techniques. J. Invest. Dermatol. 58 78 (1972). 6 Wilson, W. W., Quero, R. and Masters, K. J. The search for a practical sunscreen. South. Med. J. 59 1425 (1966). 7 Parrish, J. A., Pathak, M. A. and Fitzpatrick, T. B. Facial irritation due to sunscreen products. Arch. DerrnatoL 111 525 (1975). 8 Frosch, P. J. and Kligman, A.M. A method for appraising the stinging capacity of topically applied substances. J. $oc. Cosmet. Chem. 28 197 (1977).

J. $o½. Cosmet. Chern. 29 651-655 (1978) The leaching of F.D. & O. Blue No I dye from its lake by eleotrelytes N. A. ARMSTRONG, A. BIALKOWSKA and J. SMITH The Welsh School of Pharmacy, University of Wales Institute of Science and Technology, Cathays Park, Cardiff Presented at the Symposium on 'Product Formulation' 11 October 1978 at Harrogate Synopsis The effect of electrolyte solutions on the alumina lake of F.D. & C. Blue No 1 dye has been studied. Monovalent anions and cations cause a fairly rapid leaching of the dye for a period of about 1 h, fol- lowed by a much slower elution process. Multivalent cations cause a slight increase in leaching, but a more marked effect is obtained with salts of multivalent acids, where the dye is virtually completely removed from its substrate in 2-3 h. The results are explained by reference to the postulated structure of the alumina substrate of the lake, and the effects of pH on and ionic penetration into this structure. INTRODUCTION Though the use of water soluble dyes is common in cosmetics and pharmaceuticals, any process which involves. the use of a moving solvent front may give rise to uneven colour distribution as the dye travels with the solvent. Thus, on drying for example, dye will be transferred progressively to the surface from which evaporation is taking place, resulting in an excess of dye at that point, whilst leaving a deficiency elsewhere [Jaffe and Lipp- mann (1) Armstrong and March (2)]. The use of the lake of the dye, in which the dye is adsorbed on to an insoluble substrate, is often recommended to avoid this problem, and was used with some success by Armstrong and March in an attempt to produce uniformly coloured tablets containing F.D. & C. Blue No 1 dye. It was noted, however, that under certain conditions, for example when the tablets contained calcium phosphate, no reduction in dye migration took place. Goodhart, Everhard and Dickcius (3) found a similar effect using F.D. & C. Red No 3 dye lake in the presence of calcium sulphate, implying that ionic species presence in the system may remove the dye from its insoluble substrate. Accordingly, the role of electrolytes in displacing F.D. & C. Blue No 1 dye from its substrate has been investigated. EXPERIMENTAL MATERIAL S F.D. & C. Blue No 1 dye Batch X7663 D. F. Anstead Ltd, F.D. & C. Blue No 1 lake Batch X8432, D. F. Anstead Ltd, pure dye content, 13•o. Both substances were used without further purification. All other reagents were of Analar or laboratory reagent quality, and solutions were prepared from water which had been distilled from glass subsequent to deionisation. 0037-9832/78/1000-0651 $02.00 ¸ 1978 Society of Cosmetic Chemists of Great Britain 651