J. Soc. Cosmet. Chem. 25 23-31 (1974) ¸ 1974 Society of Cosmetic Chemists of Great Britain The substantivity of cosmetic ingred- ients to the skin, hair and teeth N.J. VAN ABBE* Presented on the 12th February 1973 in London, at the Symposium on 'Some surJbce chemical aspects of cosmetic and toiletry products', organized by the Society of Chemical Industry and the Society of Cosmetic Chemists of Great Britain. Synopsis--SUBSTANTIVITY conveys the idea of prolonged association between a material and a substrate, an association which is greater or more prolonged than would be expected with simple mechanical deposition. This review is intended to discuss the advantages and disadvan- tages of substantive effects, various ways of achieving substantivity and methods for its detection and assessment. THE NEED FOR SUBSTANTIVITY Lipstick is a typical example of decorative make-up which is left at the site of application for many hours. The effect of pigmentation is mainly achieved by purely mechanical deposition. In much the same way, various 'toiletries' are applied in a matter of seconds, or perhaps for a minute or two we then expect them to have an effect throughout the whole day or even longer. However, such preparations --for example, shampoos and toothpastes--are often rinsed away with copious amounts of water immediately after application. Sunscreens are not deliberately rinsed off in this way, but they are expected to retain their screen- ing effect even after the body has been completely immersed in seawater. So it is evident that substantivity could be extremely helpful in the cosmetic and toiletries field, to assist in providing long-lasting benefits. * Beecham Products, Applied Research and Evaluation Unit, Randalls Road, Leatherhead, Surrey. 23

24 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Clearly, the duration of effect may be even more important with so-called 'active' constituents. In practice, the need for clear evidence to show a substantive effect often becomes most obvious when the claims for a new cosmetic have to be justified to an adjudicating body. For example, an advertisement for a deodorant may suggest that one application will guard against perspiration odour for several hours evidence to substantiate such a claim will almost certainly be requested. Another example of the need for substantivity is the inclusion of an anticaries agent in a dentifrice. de Boever and Muhlemann (1) have shown that carious damage or dental decay is probably the result of long-term maintenance of a low pH inthe layer of plaque on the enamel. It follows from this that a prophylactic agent to counteract the acidity of the plaque, has to be persistent during a major part of the interval between toothbrushings. An antibacterial system, to control the plaque bacteria, also needs to show persistence in the oral cavity. This might be achieved by way of sub- stantivity to the dental enamel or to its organic coatings or to the oral soft tissues. L6e, Mandell, Derry and Schiott (2) have claimed successful results with chlorhexidine mouthrinses in plaque control and in calculus or tartar prevention. Recently, a clinical study on young adults has also shown significant reduction in dental plaque, using a mouthrinse containing 0.035•o of alexidine, an ethyl hexyl-bisguanide (3). One of the reasons for selecting this compound was its adsorption to dental enamel, which presumably helped to ensure its prolonged antimicrobial action. On the other hand, the usual idea that antimicrobial activity is the main requirement for dealing with the dental plaque has recently been challenged. A group working at the University of Tennessee (4) prepared a series of compounds representing dissected segments of the chlorhexidine molecule. They then proceeded to show that the adsorption of the chlorhexidine congeners on to hydroxy-apatite is closely matched by their surface activity in water or in a hexane-water system. In the view of these authors, anti- microbial activity may be less important than the surface-active effect of chlorhexidine they suggest that this may help to dissipate cohesive and adhesive forces in the dental plaque. The hair, once it has emerged from the scalp, is no longer a living tissue, but the concept of substantivity is still relevant. Hair-dyeing is an obvious example of a substantive process. The distinction between temporary, semi- permanent and permanent hair dyes simply indicates different degrees of substantive effect.