H. I. Maibach

Elastic properties of human skin: relation to age, sex, and anatomical region

SummaryUsing a recently developed noninvasive, in vivo suction device for measuring skin elasticity, we evaluated age, sex, and regional differences in the viscoelastic properties of skin. A total of 33 volunteers participated in the study consisting of (a) 8 young females, (b) 9 old females, (c) 8 young males and (d) 8 old males. Measurements were performed on 11 anatomical regions; three different loads were applied: 100,200, and 500 mbar. The parameters used were: immediate distension (Ue); delayed distension (Uv); immediate retraction (Ur); and, final deformation (Uf). To compare between subjects and anatomical regions, relative parameters independent of skin thickness were calculated: Uv/Ue, the ratio between the viscoelastic properties of skin and immediate distension, and Ur/Uf, which measures the ability of the skin to regain its initial position after deformation. Generally, Uv/Ue increased while Ur/Uf decreased with aging. Responses were variable with respect to load applied. Variability within anatomical regions was also noted. However, differences between the sexes were not statistically significant for most regions. These findings are in congruence with earlier studies suggesting the differences are mainly attributable to alterations in the elastic fiber network. This procedure provides a simple, quantitative assessment of elastic properties of the skin. Its application may help in future investigations of other connective tissue disorders.

Frictional properties of human skin: relation to age, sex and anatomical region, stratum corneum hydration and transepidermal water loss.

Differences in the dynamic skin friction coefficients (μ) were investigated with respect to age, sex, and anatomical region. A total of 29 volunteers consisting of seven young females, seven old females, seven young males, and eight old males participated in the study. Measurements were obtained from II anatomical regions, namely, the forehead, upper arm, volar and dorsal forearm, postauricular, palm, abdomen, upper and lower back, thigh, and ankle. The friction data were compared with stratum corneum hydration and transepidermal water loss (TEWL). The dynamic friction coefficient did not vary significantly between age and sex groups but varied considerably among the anatomical regions of the body. The forehead and postauricular had the highest μ (0.34 ± 0.02) while the abdomen had the lowest (0.12 ± 0.01); the remaining regions had an average μ value of 0.21 ± 0.01. Similarly, no sex differences were observed for TEWL and stratum corneum hydration. Capacitance was only significantly lower on the palms of the elderly. Regional differences showed a higher state of hydration on the forehead and postauricular as well as the upper arm, upper and lower back when compared with the volar forearm. TEWL was generally lower in the elderly on all anatomical regions except the postauricular and palm. A significant correlation was established between μ and capacitance for most regions. Between μ and TEWL significant correlation was observed only on the palm and thigh. These findings suggest that frictional properties of skin are dependent on more than water content or non‐apparent sweating and the role of sebum secretion is suggested as one possible factor.

Patch testing with fragrances: results of a multicenter study of the European Environmental and Contact Dermatitis Research Group with 48 frequently used constituents of perfumes

The objective of this study was to determine the frequency of reactivity to a series of commonly fragrances in dermatological patients. A total of 48 fragrances (FF) were chosen, based on the publication of Fenn in 1989 in which the lop 25 constituents of 3 types (1. perfumes, 2. household products, 3. soaps) of 400 commercial products on the US market had been determined. In a pilot study on a total of 1069 patients in 11 centres, the appropriate test concentration and vehicle were examined. For most fragrances, 1% and 5% were chosen, and petrolatum proved to be the best vehicle in comparison to isopropyl myristate and diethyl phthalate. In the main study, a set of 5 to 10 fragrances at 2 concentrations was patch tested in each centre on a minimum of 100 consecutive patients seen in the patch test clinic. These patients were also patch tested to a standard series with the 8% fragrance mix (FM) and its 8 constituents. In patients with a positive reaction to any of the 48 FF, a careful history with regard to past or present reactions to perfumed products was taken. A total of 1323 patients were tested in 11 centres. The 8% FM was positive in 89 patients (8.3% of 1072 patients). Allergic reactions to the constituents were most frequent to oak moss (24), isoeugenol (20), eugenol (13), cinnamic aldehyde (10) and geraniol (8). Reactions read as allergic on day 3/4 were observed only 10 × to 7 materials of the new series (Iso L: Super® (2), Lyral® (3), Cyclacet® (1), DMBCA (1), Vertofix® (1), citronellol (1) and amyl salicylate (1)). The remaining 41 fragrances were negative. 28 irritant or doubtful reactions on day 3/4 were observed to a total of 19 FF materials (more than 1 reaction: 5% citronellol (2), 1%amyl salicylate (2), 1%isononyl acetate (3), 0.1% musk xylol (2). 1%citral (2), and 1% ionone beta (2)). Clinical relevance of positive reactions to any of the FF series was not proved in a single case. This included the 4 reactions in patients who were negative to the 8% FM. In conclusion, the top 25 fragrances commonly found in various products caused few reactions in dermatological patients and these few appeared to be clinically irrelevant, with the possible exeption of Lyral®. However, this data should be interpreted in the light of the relatively small number of patients tested (only 100 in most centres).

Cutaneous sodium lauryl sulphate irritation potential: age and regional variability

To investigate differences in response to irritation according to age and site seven young‐adult and eight elderly females were exposed to 0.25% sodium lauryl sulphate (SLS) under patch‐test occlusion for 24 h. Ten anatomical regions were tested: forehead, upper arm, volar and dorsal forearm, postauricular, palm, abdomen, upper back, thigh, and ankle. The skin responses were evaluated 24 h post‐patch removal by visual scoring and by transepidermal water loss measurements (TEWL). Non‐treated symmetrical anatomical regions served as controls. SLS induced a mild erythematous reaction on most anatomical regions except the palm and TEWL was significantly increased as compared with controls. The elderly group demonstrated significantly less susceptibility to SLS‐induced irritation for most regions of the body as indicated by visual scores and TEWL measurements. In addition, evaluation of the stratum corneum water content following SLS irritation demonstrated lower responses in the old age group for most regions. The thigh had the highest reactivity and the palm the lowest, in both age groups. These data suggest that young adult skin is more sensitive to SLS than old skin and that SLS irritation varies considerably with respect to region. Moreover, objective TEWL measurements seem to be a better indicator of irritant susceptibility, especially in the elderly, than clinical evaluation by visual scoring.

Racial differences in sodium lauryl sulphate induced cutaneous irritation: black and white

The different reactivity of black and white skin after exposure to sodium lauryl sulphate (SLS) has been investigated. 9 white and 10 black male volunteers entered the study. The tests were performed on the back at 3 sites: untreated skin, skin pre‐treated with occlusion and skin pre‐delipidized. Irritant reactions were elicited applying 0.5% and 2.0% SLS via Finn chamber patch tests and monitored by means of laser Doppler velocimetry (LDV), transepidermal water loss (TEWL) and stratum corneum water content (WC). Higher TEWL, LDV, and WC values were recorded for 2.0% SLS when compared to 0.5% SLS and baselines. Pre‐treatment with short‐term occlusion generally increased values, while delipidization produced flattening of the data more detectable in whites than in blacks. Significant TEWL differences for the two concentrations were recorded in whites for the occluded site (P<0.02) while in blacks in the untreated (P<0.04) and delipidized (P<0.03) sites. LDV revealed significant changes in the untreated and pre‐occluded white skin (p<0.05 and 0.01, respectively). In blacks, the values were significantly different only in the pre‐occluded skin (P<0.01). Water content correlated with the visual score and was greatly increased in sites with strongly positive reactions (P<0.01). It appears that there are significant differences in the modulation of irritation, in the behavior of water barrier function and of the erythematous response between black whites. Clinical correlations are discussed.

Mechanical properties of human forearm and vulvar skin

Using a newly developed suction device, the mechanical properties of forearm and vulvar skin were studied in 22 healthy women, 12 before and 10 after the menopause. The ratio between viscous deformation (Uv) and elastic deformation (Ue) and the biological elasticity, i.e. the ratio between immediate recovery (Ur) and total deformation (Uf), were both significantly lower in vulvar than in forearm skin. Ur/Uf decreased significantly with load in vulvar, but not in forearm skin, whereas Uv/Ue was not load‐dependent in either site. Uv/Ue remained constant with age in both test sites, whereas Ur/Uf was significantly lower in post‐menopausal women in both forearm and vulvar skin. In vulvar, but not in forearm skin, Uv/Ue was significantly correlated with body height which may be an indicator of mechanical connective tissue properties. Viscous deformation plays a lesser role and biological elasticity is decreased in vulvar compared to forearm skin. Despite differences in mechanical parameters at both sites, age‐related changes seem to be similar.

Regional variation in percutaneous absorption in man: measurement by the stripping method

SummaryThe influence of anatomic site on the relationship between total penetration of a molecule and its quantities present in the stratum corneum (SC) 30 min after application was quantified in an in vivo study. For each site, six male volunteers received two symmetrical applications of 1,000 nmol benzoic acid 14C to an area of 1 cm2 for 30 min. The first application permitted measurement of total absorption of benzoic acid within 4 days (urinary excretion method), while the second enabled determination of the quantity of benzoic acid in the SC at the end of the application time. Total penetration according to site is: back < arm < chest < thigh < abdomen < forehead, (with the forehead being three times more permeable than the back). Whatever the sites and the origin of the differences observed, the results show that the single measurement of the amounts of a compound present in the SC at 30 min postapplication appears sufficient to predict its total penetration, these two parameters being linearly correlated (r=0.97, P<0.001).

Frictional properties of human forearm and vulvar skin: influence of age and correlation with transepidermal water loss and capacitance.

The dynamic friction coefficient between skin and a Teflon probe and its correlation with age, body weight, height, transepidermal water loss and skin capacitance was studied in vulvar and forearm skin of 44 healthy female volunteers. The friction coefficient of vulvar skin was 0.66 +/- 0.03 (mean +/- SEM) compared to that of forearm skin of 0.48 +/- 0.01. The difference was highly significant (p less than 0.001). Multiple-regression analysis showed that the vulvar skin friction coefficient was significantly correlated with capacitance as an indicator of stratum corneum hydration (p less than 0.01) but not with age, weight, height or transepidermal water loss. It is concluded that the high friction coefficient of vulvar skin may be due to the increased hydration of vulvar skin. Age-related differences seem to exist for transepidermal water loss and friction coefficient in forearm but not in vulvar skin.

Prevalence of patch test results from 1970 to 2002 in a multi-centre population in North America (NACDG)

Background:  The North American Contact Dermatitis Group (NACDG) has members who assess subjects with suspected allergic contact dermatitis (ACD) and patch tests them with the same screening allergens using a standardized procedure permitting analysis of long‐term trends in patch test reactions.

In vivo percutaneous absorption of fragrance ingredients in rhesus monkeys and humans

The percutaneous absorption of the fragrance diethyl maleate was measured in vivo in human and monkey studies. With the application sites occluded, 54% of the applied dose of the volatile fragrance penetrated human skin in 24 hr compared with 69% absorption in the monkey skin. It was concluded that the monkey is a good model for human skin with regard to the penetration of this fragrance material since no significant difference in the absorption of diethyl maleate was observed. The percutaneous absorption of the fragrances benzyl acetate and five other benzyl derivatives (benzyl alcohol, benzyl benzoate, benzamide, benzoin and benzophenone) was determined in vivo in monkeys. Absorption through occluded skin was high for all compounds (approximately 70% of the applied dose in 24 hr) and no significant differences between the values for the different compounds were observed. No correlations were seen between skin penetration of these compounds and their octanol-water partition coefficients. Under unoccluded conditions skin penetration of the fragrances was reduced and there was great variability between compounds, presumably because of variations in the rates of evaporation from the site of application. The data suggest that humans may have significant systemic exposure to these fragrance materials.