Abstract Frostbite of the face and ears is a common problem in cold winters. Application of an emollient on the face is a traditional way to prevent frostbite in Finland. The preliminary results of an epidemiological study on frostbite in Finnish conscripts unexpectedly showed that the use of cold protecting emollients increased the risk of facial frostbite. This finding motivated studies on the effects and use of cold protecting emollients. 830 male Finnish conscripts answered a questionnaire concerning the use of cold protecting emollients, subjective experience of using them in cold and cumulative incidence of frostbite in the ears and face. Risk factors of frostbite were investigated in a prospective epidemiological study including 913 Finnish conscripts needing medical attention for frostbite of the ears or face and their 2478 matched, uninjured controls. Thermal properties of four different emollients were studied in vitro with a skin model and in vivo in experimental cold exposures of test persons. Test emollient was applied on one half of the face, as the other half acted as control. The skin temperatures of the face-halves were compared symmetrically by thermistors and infrared thermography. Subjective sensation of thermal half-difference was also registered. 21% of the conscripts had used emollients in the cold, a majority with an experience of protection. 47% of the conscripts had had frostbite in the head (42% in the ears and 23% on the face). There was a statistically significant correlation between the use of emollients and the incidence of facial frostbite in both epidemiological studies. Applying protective emollients formed an independent risk factor for frostbite of the cheeks, nose and ear lobes (odds ratios 3.3-5.6). The thermal insulation of test emollients on the skin model was minimal. On living skin, the applied half was somewhat cooler in a majority of comparisons. However, white petrolatum gave often a subjective perception of a warming effect. False sensation of safety may form the principal cause for the increased risk of frostbite associated with the use of emollients. When the warning symptoms of cold are weak, necessary protective measures are not carried out.

L’émulsifiant est une matière première largement utilisée dans les systèmes formulés de type émulsion. Grâce à sa structure chimique amphiphile, cette molécule diminue la tension interfaciale entre les deux liquides non miscibles qui composent une émulsion, ce qui augmente la stabilité du système dans le temps. En plus, à cause de sa structure, il peut former des cristaux liquides dans les systèmes formulés, ce qui impacte considérablement les propriétés physico-chimiques et applicatives des émulsions. Ce projet vise l’étude d’un tensioactif mixte naturel alkyl polyglucoside/alcool gras. Les propriétés de celui-ci ont été d’abord investiguées via la construction du diagramme de phase. Ainsi, il a été démontré que la variation de la concentration et du ratio alkyl polyglucoside/alcool gras dans l’émulsifiant mixte favorise le passage de solutions micellaires vers les cristaux liquides de types lamellaire ou hexagonale dans les systèmes étudiés. La maitrise des propriétés des systèmes binaires a permis, par la suite, de comprendre les métamorphoses subies par le système lorsqu’une phase grasse est incorporée. La structure chimique des émollients (présence des hétéroatomes) affecte l’organisation des cristaux liquides formés par les molécules amphiphiles. Par conséquent, en fonction de l’émollient utilisé, les propriétés microscopiques et macroscopiques des systèmes changent (taille et distribution des gouttelettes, profil rhéologique, thermique et de texture). Finalement, les propriétés applicatives des émulsions sont aussi affectées, comme cela a été montré via l’analyse sensorielle et les mesures biométriques in-vivo. / Emulsifier is a raw material widely used in formulated systems of emulsion type. Due to its amphiphilic chemical structure, this molecule decreases the interfacial tension between two immiscible liquids that form an emulsion, which increases the stability of the system over time. In addition, it can form liquid crystals in the formulated systems because of its structure and this has a considerable impact on the physicochemical and applicative properties of emulsions. The objective of this project is to study a natural alkyl polyglucoside/fatty alcohol mixed surfactant. Its properties were first investigated via the construction of the phase diagram. Thus, it has been shown that the variation of the concentration and of the ratio of alkyl polyglucoside/fatty alcohol in the mixed emulsifier favors the transition between the micellar solutions towards liquid crystals of lamellar or hexagonal type in the studied systems. Next, the mastering of the binary systems properties allowed understanding the metamorphoses undergone by the system when an oil phase is incorporated into it. The chemical structure of emollients (presence of heteroatoms) affects the organization of liquid crystals formed by the amphiphilic molecules. Therefore, depending on the emollient type, the microscopic and macroscopic properties of the systems change (droplet sizes and distribution, rheological, thermal and texture profile). Finally, the applicative properties of emulsions are also affected, as shown by sensory analysis and in-vivo biometric measurements.