Reduced barrier efficiency in axillary stratum corneum A.Watkinson  , R. S. Leey, A. E. Moore  , P. D. A. Pudney  , S. E. Patersony, A.V. Rawlingsy  UnileverR&D,ColworthHse,Sharnbrook,MK441LQ; yUnileverR&D,PortSunlight,WirralL633JW,UK Received21December2001,Accepted1February2002 Keywords: antiperspirant,deodorant,sweat,TEWL,underarm Synopsis Theskinoftheaxillaiscosmeticallyimportantwith millionsofconsumersdailyapplyingantiperspirant/ deodorant products. Despite this, weknow virtually nothing about axillary skin or how antiperspirant (AP)useimpactsuponit.Tocharacterizetheaxillary stratum corneum and determine whether this is a uniqueskintype,wehavelookedatstratumcorneum composition and function, particularly its barrier properties, and compared it with other body sites. Transepidermalwaterloss(TEWL)andcorneosurfa- metry (CSM) revealed a reduced barrier function in the axilla. HPTLC analysis of the stratum corneum lipids demonstrated statistically elevated levels of fatty acids, ceramides, and particularly cholesterol in the axilla. Both ceramide and cholesterol did not appear to change with depth, indicating that they were predominantlyof stratum corneum origin. On the other hand, at least some of the fatty acid had a sebaceous origin.We hypothesized that the reduced barrier function might be owing to the changes in the crucial ceramide: cholesterol ratio. To address this,weusedacombinationofattenuatedtotalre£ec- tance^Fourier-transformed infrared spectroscopy (ATR^FTIR) with cyanoacrylate sampling. These results demonstrated more ordered lipid-lamellae phasebehaviourintheaxilla,suggestingthattheele- vated cholesterol might form crystal microdomains within the lipid lamellae, allowing an increase in water £ux. Since an exaggerated application of antiperspirant had no e¡ect upon the axilla barrier properties, it is concluded that this region of skin physiologicallyhasareducedbarrierfunction. Re ´ sume ´ La peau des aisselles est importante du point de vue cosme¤tique, avec des millions de consommateurs appliquant quotidiennement des produits antitran- spirants/de¤odorants. Malgre¤ cela, nous ne connais- sonspratiquementriendelapeaudesaissellesoude l’impact que l’utilization d’antitranspirants peut avoir surcelle-ci. A¢nde caracte¤ riserla stratum cor- neum des aisselles et de de¤terminer si elle constitue un type de peau spe¤ci¢que, nous avons examine¤ la composition et la fonction de la stratum corneum,en particulier ses proprie¤te¤s de barrie're, compare¤es a' d’autres zones du corps. La perte d’eau trans-e¤pider- mique ( trans-epidermal water loss TEWL) et la cor- ne¤osurfame¤trie (CSM) ont re¤ve¤le¤ une fonction barrie're re¤duite dans les aisselles. L’analyse HPTLC des lipides de la stratum corneum a de¤ montre¤ la pre¤ - sencedeniveauxstatistiquementpluse¤ leve¤ sd’acides gras, de ce¤ramides et en particulier de choleste¤rol dans la peauaxillaire. Ni les ce¤ ramides ni le choles- te¤rol n’ont semble¤ changer en fonction de la profon- deur, indiquant qu’ils sont probablement originaires du stratumcorneum.Cependant,aumoinsunepartie des acides gras avaient une origine se¤ bace¤ e. Notre hypothe' seestqu’unere¤ ductiondelafonctiondebar- rie'redela stratumcorneum axillaireestpeut-e“ tredue a' deschangementsdanslerapportcrucialce¤ ramides: choleste¤rol. Pour examiner cette hypothe'se, nous avons utilise¤ la spectroscopie infrarouge par trans- forme¤e de FourierATR[l’attenuated total re£ectance Fourier-transformed infrared spectroscopy (ATR^ FTIR)] combine¤e a' l’e¤chantillonnage au cyanoacry- late. Ces re¤sultats ont de¤voile¤ un comportement de International Journal of Cosmetic Science, 2002, 24, 151^161 ß 2002BlackwellScienceLtd 151 Correspondence: Dr Allan Watkinson, Unilever R&D, Colworth House, Sharnbrook, Bedford, MK44 1LQ, UK. Tel.: þ44 1234 222334; fax: þ441234 222552; e-mail: Allan.Watkinson@Unilever.com