Introduction
The first classification of skin types was proposed in 1910 by Helena Rubinstein. Skin types according to Helena Rubinstein are: dry, oily, combination, sensitive. This classification is still the current and widely used classification in the cosmetics industry. In 2006, Leslie Baumann expanded the classification of skin types by including: skin pigmentation and wrinkles. The Baumann Skin Type System (BSTS) assesses skin: hydration, sensitivity, pigmentation and aging (elasticity). The Baumann Skin Type classification is based on 4 basic, dichotomous parameters characterizing the skin: oily or dry (O vs. D), sensitive or resistant (S vs. R), pigmented or non-pigmented (P vs. N), wrinkled or tight/unwrinkled (W vs. T). There are 16 possible skin type variations (16 Baumann Skin Types). However, the Baumann Skin Types (BST) are not always static, they can vary with hormone fluctuation, pregnancy, menopause, stress, medications, lifestyle changes and climate. Therefore it is important to re-evaluate the skin type over any changes in life. The Baumann Skin Type Questionnaire (BSTQ) is an instrument developed by Leslie Baumann in 2006 to assess the skin type. The Baumann Skin Type Questionnaire is consisted of 64 questions. The 64-item self-administered questionnaire enables deriving a four-letter BSTI code (Baumann Skin Type Indicator). An individual’s BSTI four-letter code describes one of 16 possible Baumann Skin Types. Knowledge about skin type helps consumers and physicians select the most suitable skin care products for each skin type. Besides appropriate skin management, it also assists physicians in diagnosing and treating various skin conditions. Physicians can confidently recommend topical formulations which are the most appropriate for their patients’ skin type [1–4].
Furthermore, the knowledge of the skin type is important for professionals before performing medical, aesthetic and cosmetic procedures. It enables practitioners to select the most appropriate procedure, predict or avoid skin reactions and post-procedure complications [5].
One of the common cosmetic complaint is the overproduction of sebum [6]. Sensitive skin is a more complex phenomenon, quite difficult to characterize and it is becoming increasingly common [1, 7].
In the cosmetics market, there is a basic division of cosmetic products for three different skin types: oily, dry or normal. Therefore, the consumer must assess whether they have dry, oily or normal skin. In addition, cosmetic companies offer skin care products for sensitive skin, couperose skin, anti-aging and brightening products. The large selection of skin care products can confuse consumers and lead to making the wrong choice. Studies have shown that patients incorrectly assess their sebum secretion levels and in some cases believe they have oily skin even though they actually have dry skin [8, 9]. Due to difficulties in proper diagnosis of the skin type by patients, it is advisable to use a validated questionnaire for this purpose.
Aim
Originally the Baumann Skin Type Questionnaire (BSTQ) was created in English. It is valid for English-speaking patients online, and in doctors’ offices in the USA, China and Korea. BSTQ is a comprehensive questionnaire consisting of four parts: part one – oily vs. dry skin, part two – sensitive vs. resistant skin, part three – pigmented vs. non-pigmented skin and part four – wrinkled vs. tight skin [3].
Due to the fact that there is no Polish version of the questionnaire available, translation and validation of the questionnaire (part one: oily vs. dry skin and part two: sensitive vs. resistant skin) were undertaken in this study. This will enable the use of the BSTQ in further studies, in clinical practice both in dermatological and aesthetic medicine, cosmetology offices, beauty salons, during dermoconsultations in pharmacies and in remote consultations among subjects speaking Polish.
The primary objective of this study was to validate the effectiveness of the Polish language version of the Baumann Skin Type Questionnaire (BSTQ). This research aimed to ascertain the performance of the questionnaire in determining skin types according to the oily/dry, sensitive/resistant among a predominantly young adult Polish population.
Material and methods
The Polish language version of the BSTQ has been translated and validated. The consent of the Research Ethics Committee of the University of Economics and Human Sciences in Warsaw was obtained (number 02/07/2024). BSTQ in English was published with the key in 2006 in the book: “The Skin Type Solution”. The book was recognized as a national bestseller in the United States [4]. The questionnaire has attracted considerable interest and its slightly different versions can be found on the Internet.
BSTQ is used to assess skin type. The questionnaire assesses four main skin parameters: 1) oily or dry, 2) sensitive or resistant, 3) pigmented or non-pigmented, and 4. wrinkled or tight. This study discusses part one and part two of the questionnaire. The first part of the questionnaire assesses sebum production and skin hydration. It consists of 11 questions. The questions are single-choice. Each answer a is given 1 point, for answer b 2 points, for answer c 3 points, for answer d 4 points, and for answer e 2.5 points. Scoring of 27–44 indicates oily skin (O Skin Type), while scoring of 11–26 indicates dry skin (D Skin Type). The second part of the questionnaire assesses the skin’s tendency to develop pimples, redness, erythema and itching, all symptoms of sensitive skin. It consists of 18 questions. The scoring principle is the same as in the previous part, additionally, if a dermatologist diagnoses acne, rosacea, contact dermatitis or eczema, 5 points should be added to the score. If any of the above conditions was diagnosed by a doctor of another specialty, 2 points should be added to the score. Scoring of 30–72 indicates sensitive skin (S Skin Type), while scoring of 18–29 indicates resistant skin (R Skin Type) [3, 4].
Translation and validation process
The preparation of the Polish language version began with two versions of translations from English into Polish. Two independent translators translated the English version of the BSTQ into Polish. Then, the translated versions of the questionnaire were compared by a cosmetologist and a uniform version of the questionnaire was created with a minor modification. The minor modification consisted of supplementing the questionnaire with a short instruction for completion and clarifying some questions and answers for better understanding. In the next stage, another independent translator, who was not familiar with the original version of the BSTQ, performed a back translation from Polish into English. In the last stage, the original version of the BSTQ questionnaire was compared with the back translation of the Polish version (consultation with a native speaker). It was found that both versions of the questionnaire are consistent with each other in terms of content. It was assumed that the version translated from the original into Polish was created correctly.
After the translation process, the validation was performed. The questionnaire was tested on a group of 103 individuals. The participants of the study were students of cosmetology. Study participants gave written, voluntary, informed consent to participate in the study. The respondents completed the questionnaires in paper form. The questionnaire was completed by 101 women and 2 men aged 18–35 years. In order to determine test-retest reliability the respondents were asked to complete the questionnaire twice. The repeated measurement method (test-retest) was performed day after day. Due to the relatively large number of questions in the questionnaire, it is likely that the learning effect – memorizing previous answers – can be omitted.
The study respondents participated in practical classes of facial care cosmetology, which allowed for conducting interviews, skin examinations – visual and palpation skin assessment by a cosmetology expert. During 10 meetings, at weekly intervals, various facial skin care treatments were performed, which allowed for assessing the skin’s reaction to the cosmetic preparations used.
Statistical analysis
The statistical significance was determined with an a level of α = 0.05. Numerical data were summarized using the mean (M) and standard deviation (SD), while categorical data were reported as counts (n) and percentages (%). To evaluate the consistency of numerical results across test and retest measures, the intraclass correlation coefficient using a fixed effects model, ICC3, as described by Shrout and Fleiss in 1979 [10], was employed. For categorical data, the agreement was assessed using Gwet’s AC1 agreement metric, developed by Gwet in 2008 [11].
The reliability of internal consistency was assessed through several statistical methods. Cronbach’s α, both based on covariances (αraw) and correlations (αstd), initially introduced by Cronbach in 1951, was utilized [12]. Additionally, Guttman’s Lambda 6 reliability index, G6, as outlined by Kline in 1986, and the average interitem correlation (rM) were calculated [13]. The study also incorporated the index of the quality of the test, S/N, following the methodologies proposed by Cronbach and Gleser in 1964 and further refined by Revelle and Condon in 2019 [14, 15]. The standard error of Cronbach’s alpha, αSE, was calculated using the approach established by Duhachek and Iacobucci in 2004 [16]. Overall performance was estimated using accuracy, sensitivity and specificity metrics using equations (1)–(3). The global accuracy rate was calculated, accompanied by a 95% confidence interval (95% CI) for this rate, employing the binomial test.
where TPi – true positives for class i; TNi – true negatives for class i; FPi – false positives for class i; FNi – false negatives for class i.
Characteristics of the applied statistical tool
Analyses were conducted using the R Statistical language (version 4.3.1; R Core Team, 2023) on Windows 10 Pro 64 bit (build 19045) [17], using the packages irrCAC (version 1.0; Gwet (2019) [18], caret (version 6.0.94; Kuhn, 2008) [19], report (version 0.5.7; Makowski et al., 2023) [20], gtsummary (version 1.7.2; Sjoberg et al., 2021) [21], readxl (version 1.4.3; Wickham, Bryan, 2023) [22], dplyr (version 1.1.3; Wickham et al., 2023) [23], tidyr (version 1.3.0; Wickham et al., 2023) [24] and psych (version 2.3.9; Revelle, 2023) [25].
Characteristics of the sample
Table 1 offers a detailed summary of the demographic data, medical history, dermatological conditions, and cosmetic experiences of the study cohort, comprising 103 participants.
Table 1
Characteristics of the studied sample
The demographic profile of the study sample reveals a predominantly young adult population, with all participants aged between 18 and 35 years. The gender distribution is notably skewed, with females representing 98.06% of the cohort, suggesting that the findings may be more reflective of female skin health and cosmetic experiences. The majority of participants are of Polish nationality, accounting for 78.64%, followed by Ukrainians at 17.48%, and a small fraction categorized as other nationalities, which constitutes 3.88%.
In terms of medical history, the presence of systemic diseases is minimal, with only two participants reporting conditions such as diabetes and depressive-anxiety states, each affecting 0.97% of the sample. This indicates a generally healthy cohort in terms of chronic systemic conditions. A notable n = 10 (9.71%) of participants have a family history of melanoma, which could be significant in studies focusing on genetic predispositions to skin conditions.
The dermatological profile shows that n = 24 (23.30%) of the participants suffer from acne, making it the most common skin condition within the group, followed by eczema and contact dermatitis, affecting n = 10 (9.71%) and 6.80% of the sample, respectively. This suggests a moderate prevalence of common dermatological issues among the participants.
Nearly half of the study participants (44.66%) have reported experiencing skin tightening or tension after makeup removal, indicating that a significant portion of the cohort may have skin sensitivity issues related to cosmetic use. This finding is particularly relevant for cosmetic and dermatological research focusing on product sensitivity and skin barrier function.
Results
Analysis of numerical outcomes and consistency evaluation for test-retest measurements of the Baumann Skin Type Questionnaire
Table 2 provides the results of numerical outcomes for each dimension assessed by the Baumann Skin Type Questionnaire, along with a detailed analysis of the consistency in results across test-retest measurements.
Table 2
Distribution of overall numerical results in each dimension with estimates of agreement for test-retest measurements, df1 = 102, df2= 22, F = 22
This evaluation captures the distribution of mean scores (M) and their standard deviations (SD), offering a precise depiction of participant responses across two distinct skin type dimensions: oily or dry skin and sensitive or resistant skin. The table further assesses the reliability of these measurements through ICC3 values, complemented by 95% confidence intervals (95% CI) and p-values (p), thus underscoring the robustness of the questionnaire in producing consistent and reproducible results. The accompanying statistical parameters, including degrees of freedom (df1 and df2) and F-values, provide additional validation of the statistical processes employed in this consistency check.
In the dimension assessing oily or dry skin, the mean scores are closely aligned between the test (M = 27.10 with a SD = 4.75) and the retest (M = 26.67, SD = 4.86), yielding an ICC3 = 0.91. This suggests an outstanding level of reliability in repeated measurements, which is crucial for dermatological studies where skin condition variability might impact longitudinal assessments.
Similarly, the sensitive or resistant skin dimension reported even higher reliability (ICC3 = 0.96), with mean scores of M = 33.31 (SD = 7.22) during the test and M = 32.31 (SD = 7.71) at retest. The slight variations in mean scores are overshadowed by the high ICC value, reflecting robustness in the test’s ability to consistently classify this skin dimension over time.
In summary, the results in Table 2 explicitly demonstrate high consistency in the scores between the initial test and the retest, as evidenced by the ICC3 values exceeding 0.90 in the two dimensions indicated. These are supported by narrow 95% confidence intervals, indicating a high level of precision in the estimates of agreement.
For detailed descriptive statistics and the agreement rates pertaining to individual items within a specific dimension of the Baumann Skin Type Questionnaire, please refer to Supplementary Table S1.
Analysis of the internal reliability for test-retest measurements of the Baumann Skin Type Questionnaire
A meticulous analysis of the internal consistency of numerical scores for individual questions within distinct dimensions of the Baumann Skin Type Questionnaire, measured both at the test and retest stage presented in Supplementary Table S2.
The dimension Oily or Dry Skin shows a based upon the covariances (αraw) and correlations (αstd) scores of 0.75 and 0.74, respectively, during testing, which slightly improve in the retest phase to 0.77. This indicates a good level of internal consistency, corroborated by Guttman’s Lambda 6 reliability (G6) values of 0.79 initially and 0.81 at retest, suggesting robust item correlations.
Initial testing for Sensitive or Resistant Skin dimension reveals αraw and αstd scores of 0.72 and 0.74, respectively. These scores increased to 0.78 and 0.79 at retest, alongside an improvement in G6 from 0.81 to 0.85, indicating an enhanced internal consistency upon retesting.
The Baumann Skin Type Questionnaire shows high reliability. Clinicians can confidently use these classifications to recommend specific skin care products and treatments. For instance, patients identified with consistently oily skin could be advised on appropriate astringents or mattifying products, while those with sensitive skin might benefit from hypoallergenic or fragrance-free formulations.
Comprehensive evaluation of skin type results and agreement for test-retest measurements of the Baumann Skin Type Questionnaire
The results presented in Table 3 delineate a systematic evaluation of the consistency and accuracy in classifying skin types using the Baumann Skin Type Questionnaire across two measurement points. This table elucidates both the distribution of skin type classifications and the agreement rates between initial testing and retesting sessions. Each segment of the questionnaire – focusing on characteristics such as oily or dry skin, sensitivity – undergoes scrutiny to determine both the stability of the classification over time and the precision of each category’s assessment.
Table 3
The results of skin types and consistency assessment for test-retest measurements
The agreement between measures, quantified through the AC1 statistic, is complemented by standard error and confidence interval metrics, offering a robust statistical framework to understand the reliability of the questionnaire.
The data presented in Table 3 reveal significant consistency across all dimensions of skin type assessment, with AC1 values indicating agreement between initial testing and retesting sessions, which underscores the reliability of this questionnaire in clinical and research settings.
In the dimension addressing oily or dry skin, the AC1 value is 0.69, with a confidence interval ranging from 0.55 to 0.83, signalling substantial agreement. The slight shift in percentage points between the test and retest for dry and oily classifications suggests a minor variability in participant responses or in the interpretative consistency of the questionnaire over time.
The assessment of sensitive versus resistant skin shows an AC1 of 0.74, with a confidence interval from 0.61 to 0.87, indicating a higher level of agreement. This dimension shows a notable shift in classifications from resistant to sensitive between the two sessions, perhaps reflecting a subjective interpretation of skin sensitivity symptoms by the participants, which may slightly vary over time.
The slight variability observed in some dimensions may indicate the need for further refinement of the questionnaire or training for participants in identifying and reporting subtle skin condition changes.
Evaluation of skin type results via visual inspection
The analysis of the skin type characteristics based on visual inspection conducted by a specialist, as detailed in Table 4, offers significant insights into the distribution and prevalence of various skin conditions within a sample size of 103 individuals. This assessment mirrors the structure of the Baumann Skin Type Questionnaire and encompasses two distinct dimensions. The observations recorded are treated as actual data for subsequent analyses, ensuring a rigorous and structured approach to understanding skin type distributions within the observed cohort.
Table 4
Characteristics of skin types based on visual inspection across two dimensions, N = 103
| Characteristic | n (%) |
|---|---|
| Oily or dry skin: | |
| Dry | 45 (43.69) |
| Oily | 58 (56.31) |
| Sensitive or resistant skin | |
| Resistant | 47 (45.63) |
| Sensitive | 56 (54.37) |
Starting with the distribution between oily and dry skin types, there is a noticeable inclination towards oily skin, which affects 56.31% of the sample. This prevalence suggests either genetic predispositions or environmental factors that favour higher sebum production. Conversely, the cohort exhibits a nearly balanced division between sensitive and resistant skin types, with 54.37% identified as sensitive.
Evaluation of the Baumann Skin Type Questionnaire: performance metrics across different skin type classifications
The following table, designated as Table 5, presents a detailed analysis of the performance metrics for skin type classification using the Baumann Skin Type Questionnaire compared with validation by the observed data.
Table 5
Performance metrics for skin type classification (estimated vs. observed), N = 103
This assessment encompasses dimensions of skin types, including oily versus dry and sensitive versus resistant skin. The metrics provided in the table, such as accuracy, confidence intervals (95% CI), sensitivity, and specificity, are pivotal for understanding the effectiveness of the questionnaire in accurately classifying different skin conditions. Each dimension is tested and retested to evaluate the consistency and reliability of the questionnaire over repeated measures.
This rigorous analysis is crucial for dermatological research and practice, as it helps in verifying the utility of the questionnaire as a diagnostic tool in clinical settings.
For the classification of oily versus dry skin, the questionnaire demonstrates high accuracy and consistency. The initial test shows an accuracy of 96% with confidence intervals tightly ranged between 90% and 99%, accompanied by high sensitivity and specificity values of 95% and 98%, respectively. The retest, while showing a slight decrease in accuracy to 86%, still maintains strong sensitivity and specificity, indicating reliable reproducibility over time.
In the dimension of sensitive versus resistant skin, the questionnaire also shows commendable performance, with both initial testing and retesting reflecting an accuracy of 86%. The sensitivity in the initial test is notably high at 98%, though it slightly decreases in the retest to 89%. Specificity shows a substantial increase from 72% to 83% on retest, suggesting an improvement in the ability to correctly identify non-sensitive skin over repeated measures.
The results presented above proved that the Baumann Skin Type Questionnaire exhibits strong performance in classifying oily versus dry and sensitive versus resistant skin types.
The full Polish version of the BSTQ will be available in part two of the article (Baumann Skin Type Questionnaire (BSTQ): creation and validation of the Polish language version – part two).
Discussion
A proper skin type classification is very important both for consumers and professionals. It enables to select the most appropriate skin care products, skin care protocols, aesthetic and cosmetic procedures. However, its importance in clinical research cannot be forgotten. The aim of correct and careful skin type classification is improving clinical approach to skin condition [5, 26].
Studies show that patients cannot correctly self-diagnose their own skin type, therefore it is advisable to use the Baumann Skin Type Questionnaire for that purpose [3, 9, 27]. A properly validated questionnaire is an important complementary diagnostic instrument in clinical practice.
This study describes a detailed process of development and validation of the Polish language version of the BSTQ (part one: oily vs. dry skin and part two: sensitive vs. resistant skin). Comparing to the original version of the BSTQ regarding skin oiliness, the translated Polish language version showed similar internal consistency reliability (value of Cronbach α coefficient = 0.78 vs Polish language version: αraw = 0.75, αstd= 0.74 in test and in retest: αraw = 0.77, αstd = 0.77) [6]. Cronbach α coefficient of at least 0.7 indicates sufficient questionnaire internal consistency [12].
The main limitations were the validation of the BSTQ on an undifferentiated study sample and the results may be different for the entire Polish population. It would be reasonable to revise the questionnaire in the future with a larger and more diverse group in terms of age and gender.
Conclusions
The Baumann Skin Type Questionnaire, when evaluated for classification performance across various skin type dimensions, provides a robust tool in diagnosing oily or dry skin and sensitive or resistant skin. Specialists can confidently use these classifications to recommend specific skin care products and treatments.
