434 R. Marks This is important to remember as it should help in designing techniques for the evalu- ation of emollients. Keratolytics are even less appropriately named. This term taken literally signifies a material which 'lyses keratin'. It should not be necessary to remind you that keratin is an intracellular alpha fibrous protein suspended in a matrix of unknown composition and surrounded by the tough plasma membrane of the corneocyte wall. It seems most unlikely that this component is involved in the action of keratolytics. We probably mean by 'keratolytic' an agent that enhances desquamation. It is even more confusing when one realises that by enhancing desquamation one may also 'smooth' so that keratolytics may be also emollients! We probably need different terms and new definitions and I would suggest that we come nearer to the actual action that we seek in choosing them. If we drop the term 'emollient' and substitute 'hydrating agent' we more accurately describe the action of these substances and can define them as agents whose action is to smooth the surface by hydrating it and which is reversible and short lived. 'Descaling agent' is more appropriate than 'keratolytic' and this term may be defined as a substance that acts irreversibly to alter abnormal desquamation such that hyperkeratosis and scaliness are decreased. Thus, water is only a 'hydrating agent' and not a 'descaling agent', even though it may enhance desquamation in the short term, because its action is reversible and short lived. Similarly, salicylic acid is purely a descaling agent as although it may 'smooth' it does not hydrate and its action is irreversible. HYDRATING AGENTS (HA) (a) SUBJECTIVE TECHNIQUES The palparing finger and the eye are remarkably sensitive and the user of the HA or the clinical observer can easily tell whether the skin is more or less smooth than before application. This effect cannot be accurately quantified, however, and is subject to 'bias' and the placebo effect. Middleton and Roberts (2) optimised this method during the evaluation of a 'hand cream' containing PCA, by employing a 'double blind technique' and a complex clinical scoring system. We have also been able to show that there is a difference in the 'clinical score' after the use of an emollient cream for 1 and 2 weeks in twenty patients with dry skin (Table I). Although these results are not statistically significant the trends are undeniable. Table L Results of use of aqueous cream on skin 'dryness' in subjects with dry skin Time (weeks) Subject assessment* Observer assessmenr[' 0 2.2+0.9 1 1'6+0'8 3.1+0.9 2 1-8+0.9 3.4+0.7 * Mean and S.D. of arbitrary scores: 1 = 25•o, 2 =25-50•o, 3 = 50•o improvement. -1' Mean and S.D. of arbitrary scores: 1 =very dry and scaly, 2 = moderately dry and scaly, 3 =slightly dry, 4 =normal. (b) MORPHOLOGY The simplest morphological technique is that of macrophotography. Here the surface of

Figure 1. Scanning electron micrograph of a replica taken from skin treated with an HA 2 h previously. Notice shallow skin furrows. (x 16.5). v.. .- .:. •,, . • , .... . , • . ..... • • • •-C ' ..... '-• -.. .. ..... .- • • • . -•-•. " .•.. •'•.' -•..%. •'•'. •... 2 • • •,: •.• •.'.• •,• .• -,•--: -.-•,• . ...... • .i.... ".•'• • - ...... . . - , - .•. .:% •-•. : • . . • . • •.' - '•'•,•.?' %.... •? ...? - . ..... . •.-..:. Figure •. Scanning electron micro•aph of replica of skin surface treated with HA 2 h previously. Notice prominent cell borders and thickened individual corneocytes. (x 1-28 K). Facing page 43•