Seborrheic dermatitis (SD) is a common chronic recurring inflammatory skin disease located in seborrheic area. It affects 2.35%–11.3% of the general population [
The stratum corneum plays a crucial role as the skin barrier in regulating metabolic processes and functions. By measuring various biophysical properties of the stratum corneum, several studies report abnormal biophysical profiles and their association in various dermatologic diseases, such as atopic dermatitis (AD) and psoriasis. Compared to healthy population, various abnormal profiles such as increment in transepidermal water loss (TEWL) or reduction in stratum corneum hydration (SCH) were found in patients with these diseases [
Scalp skin reveals a remarkable difference to the skin of other body regions. It comprises an abundance of hair follicles, sebaceous glands, and blood vessels, resulting in the dissimilarity of its biophysical properties compared to other parts of the body. To our knowledge, the biophysical profiles of scalp SD have never been investigated. Better understanding of their profiles may help establish the pathophysiology of the disease, assess the treatment efficacy, and improve the patient care. The aim of the study is to analyze the biophysical and physiological properties of scalp SD compared to healthy controls.
This study is a cross-sectional study assessing the correlation of various biophysical profiles in scalp SD. The study was approved by the Committee of Human Rights Related to Research Involving Human Subjects, Mahidol University (ID03-59-19). The study adhered to the principles of the Declaration of Helsinki. All patients provided written and witnessed informed consent.
The sample size was estimated based on data from a previous study of TEWL and water content in the stratum corneum in SD [
Both SD and control groups were subjected to a one-time biophysical and physiological properties’ measurement. All participants were informed to avoid all types of hair and scalp products 12 hours prior to the examination. The measurement was performed by a well-trained and experienced investigator under standardized condition (temperature of 19°C–24°C and relative humidity of 50%–58%). All participants were in the measurement room for at least 15 minutes before the measurement for acclimatization.
Area with clinical evidence of SD on the scalp was chosen to be measured in SD group while occipital area of the scalp was chosen in control group. TEWL was measured using Tewameter® TM 300 (Courage + Khazaka electronic GmbH, Köln Germany), SCH was measured by Corneometer® CM 825 (Courage + Khazaka electronic GmbH, Köln Germany), skin surface pH was measured using Skin pH meter® PH 905 (Courage + Khazaka electronic GmbH, Köln Germany), skin surface lipid was measured by Sebumeter® SM 815 (Courage + Khazaka electronic GmbH, Köln Germany), and, lastly, skin roughness was assessed by Visioscan® VC 98 (Courage + Khazaka electronic GmbH, Köln Germany). Three readings of each measurement were made. All measurements were done on the same area and location. The mean values were then calculated from these readings.
For further analysis purpose, we asked a blinded dermatologist to categorize scalp SD cases into mild, moderate, and severe using 4-point scale scores which rate each scalp in terms of erythema (0 = no erythema, 1 = faint pink color, 2 = pink color, and 3 = red color), dandruff (0 = no dandruff, 1 = only scrapped, 2 = obvious scaling, and 3 = obvious sheets), and lesional extent (0 = no lesion, 1 = 1–30% of scalp area, 2 = 31–70% of scalp area, and 3 = 71–100% of scalp area). The sum of these components was obtained which classified each participant into mild (1–3), moderate (4–6), or severe SD (7–9) [
Statistical analysis was performed using SPSS for Windows, version 18.0 (SPSS Inc., Chicago, IL, USA). The data were not analyzed separately for male and female participants as the preliminary analysis revealed no statistically significant difference in outcomes between genders. Categorical data, mainly sex, was expressed as proportions and was analyzed using chi-squared test. Continuous variables were expressed as mean ± standard deviation and the mean age was analyzed using t-test while measured variables were evaluated using analysis of variance with post hoc Tukey Honestly Significant Difference test. Disease duration among subgroups was compared using Kruskal–Wallis test. P value of less than 0.05 was considered to be statistically significant.
The participants’ demographic data is summarized in Table
Demographic data.
Variables | Case (n = 42) | Control (n = 40) | P value |
---|---|---|---|
| |||
mean ± SD | 34.5 ± 6.9 | 32.4 ± 6.6 | 0.16 |
| |||
Male | 15 (35.7%) | 12 (30.0%) | 0.58 |
Female | 27 (64.3%) | 28 (70.0%) | |
| |||
median (range) | 4 (1-11) | - | NA |
| |||
Frontal | 4 | 0 | NA |
Vertex | 9 | 0 | |
Parietal | 15 | 0 | |
Occipital | 14 | 40 |
Biophysical properties of scalp seborrheic dermatitis cases and control.
Variables | Case | Control | 95% CI | P value |
---|---|---|---|---|
(n = 42) | (n = 40) | |||
| ||||
mean ± SD | 13.91 ± 4.52 | 11.66 ± 3.93 | 0.44 - 4.15 | <0.05 |
| ||||
mean ± SD | 5.61 ± 1.24 | 6.42 ± 1.92 | -1.49 - -0.10 | <0.05 |
| ||||
mean ± SD | 4.95 ± 0.51 | 5.19 ± 0.62 | -0.44 - 0.04 | 0.104 |
| ||||
mean ± SD | 35.63 ± 7.59 | 29.56 ± 6.35 | 3.04 - 9.15 | <0.05 |
| ||||
mean ± SD | 11.55 ± 3.56 | 10.85 ± 2.61 | -0.66 - 2.06 | 0.308 |
Through performing subgroup analysis, the mean skin surface lipid was found to be directly proportional with disease severity (
Biophysical properties among various severity of scalp seborrheic dermatitis cases and control.
Variables | Mild (n = 14) | Moderate (n = 16) | Severe (n = 12) | Control (n = 40) | P value |
---|---|---|---|---|---|
| |||||
mean ± SD | 33.5 (5.5) | 36.1 (6.9) | 34.9 (6.4) | 32.4 (6.6) | 0.24 |
| |||||
male:female | 6:8 | 5:11 | 4:8 | 12:28 | 0.84 |
| |||||
median (range) | 4 (1-10) | 3.5 (1-11) | 4 (1-9) | - | 0.96 |
| |||||
mean ± SD | 13.52 ± 4.65 | 13.89 ± 4.91 | 14.25 ± 5.24 | 11.66 ± 3.93 | 0.16 |
| |||||
mean ± SD | 6.25 ± 1.24 | 5.91 ± 1.19 | 5.46 ± 1.25 | 6.42 ± 1.92 | 0.25 |
| |||||
mean ± SD | 4.92 ± 0.46 | 5.05 ± 0.65 | 4.94 ± 0.51 | 5.19 ± 0.62 | 0.56 |
| |||||
mean ± SD | 32.41 ± 6.52 | 35.19 ± 7.95 | 35.93 ± 6.99 | 29.56 ± 6.35 | <0.05 |
| |||||
mean ± SD | 11.26 ± 3.25 | 11.91 ± 3.65 | 11.46 ± 3.59 | 10.85 ± 2.61 | 0.66 |
Pairwise comparison of skin surface lipids in participants.
Skin surface lipid | P value | Difference | 95% Confidence interval |
---|---|---|---|
Control vs. mild SSD | 0.49 | 2.91 | -2.55 - 8.35 |
Control vs. moderate SSD | <0.05 | 5.65 | 0.45 - 10.74 |
Control vs. severe SSD | <0.05 | 6.45 | 0.67 - 12.12 |
Mild SSD vs. moderate SSD | 0.68 | 2.78 | -3.66 - 9.06 |
Mild SSD vs. severe SSD | 0.53 | 3.56 | -3.34 - 10.34 |
Moderate SSD vs. severe SSD | 0.98 | 0.81 | -5.84 - 7.44 |
Scalp SD and dandruff are considered as components of the same dermatological condition that affects the scalp where SD represents a more severe and less confined presentation. Despite being a relatively common condition, the pathogenesis of SD or dandruff is still unclear [
The stratum corneum is a multilayered structure built with anucleated, flattened corneocytes which are linked by continuous specialized lipidic matrix [
Among these miscellaneous elements of stratum corneum, corneodesmosome, a specialized intercellular protein that locks the corneocytes together, plays the most crucial role in maintaining the integrity of the stratum corneum [
Scalp SD patients had increased TEWL similar to AD indicating impaired permeability function. Similar to AD, SCH of scalp SD was also found to be decreased as well [
Interestingly, the scalp SD disease severity was found to have significant positive correlation with the mean skin surface lipid in our study. More severe disease was associated with higher mean skin surface lipid. Thus, our study supports the concept of seborrhea as an etiology of SD contradicting previous studies which were inconclusive or suggesting otherwise [
The main limitation of our study is the small number of study population and being a single-center study. Furthermore, numerous influencing factors, such as sex, age, and ethnicity, may affect a standardized range or cut-off point of the biophysical and physiological parameters of scalp SD [
In conclusion, Scalp SD may be associated with seborrhea or abnormality in skin sebum properties. Monitoring of SCH, TEWL, and skin surface lipid could be helpful in assessing severity and evaluating the treatment outcome of scalp SD.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare no conflicts of interest.
All funding of this project was provided by Division of Dermatology, Department of Medicine, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Thailand.