Background/aims: Surface energy phenomena result from molecular interaction between substances. On the skin, they are involved in sweat and sebum dispersion, and in foreign substances, in spreading and absorption. However, they are unknown due to the scarce number of studies. The aim of this work was to find the skin critical surface tension (CST), an index of wettability, through a reliable technique, and to study the influence of skin lipid and of some oil-in-water (O/W) and water-in-oil (W/O) preparations.

Method: The CST was calculated using the Zisman equation, from the contact angle at equilibrium, of droplets of liquids whose surface tension was known. Contact angles were computed from the base and the height of the droplets viewed from their side through an operating microscope provided with a slanted mirror. Both volar forearm and forehead were studied.

Results: On volar forearm, the skin CST was 27.5±2.4 dyne/cm (n=12) and normally distributed. Forehead CST was above 50.7 dyne/cm. On both areas, defatting with ether reduced CST down to 21.6±2.6 dyne/cm, and 29.3±1.7 dyne/cm, respectively (p<0.001). Washing with soap reduced forearm CST down to 23.7±1.0 dyne/cm (p<0.01), and occlusion down to 21.6±3.4 dyne/cm (p<0.001). O/W cream application strongly decreased both forearm and glass slide CST, whereas W/O cream application either raised CST or left it unchanged; in all cases, changes were less marked on skin than on glass.

Conclusion: These data demonstrate that the skin surface is primarily hydrophobic and paradoxically becomes more wettable through its lipidic component, especially the sebum. Emulsions seemed to interact with the skin and change its CST as would do their continuous phase only.

Skin critical surface tension: A way to assess the skin wettability quantitatively.

Because the skin is a surface, it is convenient to analyze and describe it in terms of its surface
characteristics such as friction. Tribological studies of skin provide valuable insight into how
the skin interacts with other surfaces and how it can change under various conditions, like age
and health, and chemical treatments, such as lotions and moisturizers (1). Because the skin is
the first-line of defense against the environment, it is repeatedly subjected to physical and
chemical damage and alterations. For example, Naylor (2) showed that the moistened skin has
an elevated friction response, and El-Shimi (3) demonstrated that the drier skin has a lowered
friction response. Tribological studies offer convenient, noninvasive techniques to quantitatively assess skin health and hydration.

Tribological Studies on Skin: Measurement of the Coefficient of Friction

Biochemical and physiological examinations were carried out on the skin surface of a total of 115 healthy persons ranging from the age of 7–79 years. In these investigations the following striking findings were made:

1.

There is a significant correlation between the results obtained by the ferricyanide, the phenol sulfuric acid and the ninhydrin methods in the so called water solubles.




2.

The relationship between the fraction of wax and cholesterol esters and the squalene fraction in the skin surface lipids influences the release of free fatty acids by bacterial lipases.




3.

With regards to most parameters tested there are great differences between the 8–12 year age group and the older age groups.




4.

There are significant differences in the 8–12 year age group between the male and female test persons.




5.

With regards to the parameters tested there are also significant differences between the various test areas.

Biochemical and physiological parameters on the skin surface of healthy test persons: a contribution towards the interpretation of the results obtained by a screening program.

This is a report on biochemical and physiological examinations carried out on 20 test persons who in the last 2 years had contacted and completely recovered from pityriasis versicolor and on 25 control persons of corresponding age and sex. The tests on the skin surface of the patients with pityriasis versicolor show, when compared with the corresponding control group, the following significant results:
 It is probable that these results point to important predisposing factors for pityriasis versicolor.

Predisposing factors on the surface of the skin in persons with pityriasis versicolor

Bei der Abwehr auserlicher Einwirkungen kommt zwar stets die Gesamtheit der unterschiedlichen Strukturen und Funktionen des Hautorgans in differenzierter Weise zur Geltung. Wahrend die Lederhaut jedoch uberwiegend als Schutzhulle gegenuber physikalischen, insbesondere stumpfen mechanischen Insulten wirksam ist, bildet die Hornschicht, an der ausersten Peripherie des Korpers angelegt, eine lebensnotwendige Barriere: Sie bewahrt den Innenkorper vor Austrocknung durch ungeregelten, ubermasigen Wasserverlust an die Umwelt, und sie schutzt das Einzelwesen in weiten Grenzen gegen chemische und physikalische Mikrotraumen sowie vor schadigender kosmischer Strahlung. Unabdingbare Voraussetzung fur die Funktionstuchtigkeit des Integuments und somit fur die Berufs- und Arbeitsfahigkeit ist das Erhaltensein der Hornschicht-Koharenz. Beim Auftreten flachenhafter, grabenartiger oder auch nur punktformiger Hornschicht-Durchbruche fuhrt der Ansturm exogener Noxen zur unmittelbaren Irritation und Reaktion der betroffenen epithelialen Zellverbande und, begleitet von kutan-vaskularen Erscheinungen, zur Ausbildung einer toxischen irritativen und/oder allergischen Dermatitis, deren Verlaufszeit und Schwere die Dauer und Intensitat der ursachlichen Noxen-Einwirkung unverhaltnismasig weit ubertreffen konnen.

Arbeitsphysiologie der Hornschicht in Grundzügen

Parallele Untersuchungen mit dem Osmiumsauretest und qualitative und quantitative Bestimmungen der Hautoberflachenlipide an 51 Versuchspersonen 2 Stunden nach Entfetten der Haut mit Petrolather zeigten, das die Reaktion der Talgdrusen auf die Entfettung der Haut von Fall zu Fall, von Stelle zu Stelle und von Druse zu Druse stark unterschiedlich ist. Die Schnelligkeit und das Ausmas des Lipidersatzes scheinen sowohl von der Zahl der sezernierenden Talgdrusen als auch vom Ausmas der Sekretion der Einzeldruse abhangig zu sein. Auserdem war die Spreitflache des Talgdrusensekretes um so groser, je mehr Wachsester und je weniger Paraffine in den Hautoberflachenlipiden nachweisbar waren. Parallele Messungen der Benetzbarkeit der Haut mit Wasser und Paraffinol sowie quantitative und qualitative Bestimmungen der Hautoberflachenlipide vor und 2 Stunden nach Entfetten der Haut mit Petrolather machten deutlich, das die Benetzbarkeit der Haut mit hydrophilen und lipophilen Substanzen um so besser ist, je mehr Hautoberflachenlipide vorhanden sind. Daruber hinaus nimmt die Benetzbarkeit der Haut mit steigendem Gehalt der Hautoberflachenlipide an freien Fettsauren und sinkenden Gehalt an Paraffinen zu, wahrend ein groser Anteil an squalen und gesattigten Kohlenwasserstoffen zu einer Begunstigung der Benetzbarkeit der Haut mit Paraffinol fuhrt.

M. Gloor

Papers

Untersuchungen über die Physiologie der Talgdrüsen und über den Einfluß der Hautoberflächenlipide auf die benetzbarkeit der Haut

[Studies on the sebaceous gland physiology and the effects of skin surface lipids on skin moistening (author's transl)].