440 R. Marks REFERENCES 1 Quattrone, A. J. and Laden, K. physical techniques for assessing skin moisturization. J. Soc. Cosmet. Chem. 27 607 (1976). 2 Middleton, J. D. and Roberts, M. E. Efficacy of a skin cream containing pyrrolidone carboxylic acid in reducing the incidence of subclinical dry skin. In: Marks, R. and Dykes, P. J. The Ichthyoses. 177 (1978) MTP Press Ltd, Lancaster. 3 Garber, C. A. and Nightingale, C. T. Characterizing cosmetic effects and skin morphology by scanning electron microscopy. J. Soc. Cosmet. Chem. 27 509 (1976). 4 Bernstein, E. O. Scanning electron microscopy of skin topography before and after treatment. Ann. Meet. Soc. Cosmet. Chem. December 1974, New York City. 5 Marks, R and Dawber, R. P. R. Skin surface biopsy: an improved technique for the examination of the horny layer. Brit. •. Dermatol. 84 117 (1971). 6 Marks, R. and Pearse, A.D. Surfometry: a method of evaluating the internal structure of the stratum corneum. Brit. J. Derrnatol. 92, 651 (1975). 7 Marks, R., Nicholls, S. and Fitzgeorge, D. Measurement of intracorneal cohesion in man using in vivo techniques. J. Invest. Dermatol. 69 (3) 299 (1977). 8 Nicholls, S., King, C. S., Guibarra, E. and Marks, R. Measurement of point deformation (PD) of human skin in vivo: contribution of the stratum corneum. Ann. Meet. Eur. Soc. Dermatol. Res. Amsterdam (1978). 9 Clar, E. J., Her, C. P. and Sturelle, C. G. Skin impedance and moisturization. J. Soc. Cosmet. Chem. 26 337 (1975). 10 Edelberg, R. Relation of electrical properties of skin to structure and physiologic state. J. Invest. Dermatol. 69 324 (1977). 11 Agache, P., Boyer, J.P. and Laurent, R. Biomechanical properties and microscopic morphology of human stratum corneum incubated in a wet pad in vitro. Archiv. fiir Derrnatol. Forschung. 246 271 (1973). 12 Middleton, J. D. The effect of temperature on extensibility of isolated stratum corneum and its relation to skin chapping. Brit. J. Derrnatol. 81, 717 (1969). 13 Ferguson, J. and Agache, P. Influence of site, storage and trypsin treatment on the mechanical properties of the stratum corneum. J. Invest. Derrnatol. 68, 256 (1977). 14 Miller, D. L. and Wildanauer, R. H. Thermomechanical probes for the analysis of physical properties of stratum corneum. J. Invest Dermatol. 69 297 (1977). 15 Laden, K. & Spitzer, R. Identification of a natural moisturizing agent in skin. J. $oc. Cosmet. Chern. 18 351 (1967). 16 Rosencraig, A. and Pines, E. Stratum corneum studies with photoacoustic spectroscopy. J. Invest. Derrnatol. 69 296 (1977). 17 Van Scott, E. J. and Yu, R. J. Control of keratinization with alpha-hydroxy acids and related compounds. I. Topical treatment of ichthyotic disorders. Arch. Derrnatol. 110 586 (1974). 18 Nicholls, S. and Marks, R. Novel techniques for the estimation of intracorneal cohesion in vivo. Brit. J. Derrnatol. 96 595 (1977). 19 Davies, N. and Marks, R. Studies on the effect of salicylic acid on normal skin. Brit. J. Derrnatol. 95 187 (1976). 20 Mackenzie, I. C. and Linder, J. E. An examination of cellular organization within the stratum corneum by a silver staining method. J. Invest. Dermatol. 61 245 (1973). 21 Huber, C. and Christophers, E. 'Keratolytic' effect of salicylic acid. Arch. Derrnatol. Res. 257 293 (1977).

J. $oc. Cosmet. Chem. 29 441-446 (1978) Evaluation of mechanical stresses set up in lipstick during application R. G. DREW Beecham Products, Applied Research Laboratories, Randalls Road, Leatherhead, Surrey, KT22 7RX Received 19 January 1978 Presented as part of a lecture for the Society of Cosmetic Chemists of Great Britain, London, January, 1977 Synopsis A device is described which measures the stresses set up when lipstick is applied this device is used to assess the application properties of two ranges of commercially available lipsticks. The values obtained facilitate definition of the strength requirements of a lipstick. Knowledge of the in-use stresses will enable formulators to avoid fracture problems during lipstick application. A trial of ten commercially the available lipsticks indicates that the application force is related to the ease of colouring of the lips be applied lipstick. Application forces were greater when the lipstick was applied by older subjects. INTRODUCTION A lipstick consists essentially of a solid stick in a retractable applicator. In recent years lipstick formulations have altered considerably hard sticks with high levels of staining dye have been almost completely superseded by softer sticks in which soluble dye has been largely replaced by insoluble dye in lipsticks (pigments). With the reduction in level of staining dye in lipsticks much easier transference is required in order to achieve adequate colouration of the lips. Elliott (1) indicated that this has been achieved by introducing oilier bases. The increased liquid and semi-solid content of recent formu- lations has made the mechanical strength requirements of the stick critical. A common method of lipstick strength assessment described by Lauffer (2) is to hold the lipstick horizontally in a socket fitting over 1 cm of its base and to apply weights at a measured distance from the edge of the socket. The weight is increased by increments (suitably 0.1 N) every 30 min until the lipstick breaks. At least four readings are needed for each batch of lipstick and broken surfaces must be examined to ensure that no weakening flaws reduce the strength. Breaking point measurements must be carried out at a known temperature (suitably 25øC) on sticks stored at that temperature for at least 30 min. This technique is unrealistic as the method of loading involves a disproportionately large shear component and a small bending moment when measuring the total force to fracture. Lauffer (2) also described a method of roughly measuring the force of appli- cation. A strip of smooth paper is drawn between two flat lipstick ends at constant speed. The force required to pull the paper when a given total weight is applied to the upper lipstick is recorded. 0037-9832/78/0700-0441 $02.00 ¸ 1978 Society of Cosmetic Chemists of Great Britain 441