410 JOURNAL OF COSMETIC SCIENCE
Unlike most skin typing systems that focus solely on a single condition like dry or acne-
prone,22 the BST codifies an individual’s skin phenotype by considering multiple factors
simultaneously. This approach ensures that the skin care regimen is tailored to all of the
individual’s skin concerns—not just one—leading to improved and predictable outcomes.
SKIN TYPE QUIZ VALIDATION
The skin type quiz was validated using many methods and with collaboration among
dermatologists around the world. Validation studies of the latest quiz version are currently
being run in Indonesia, Portugal, and Africa. The original quiz had over 300 questions.
The next version was 64 questions. The latest version has 15 multiple response questions.
The questionnaire is constantly being tested, revalidated, and reformatted as worldwide
data are gathered, and as technology changes occur, such as the recent advances in AI
data analysis. The original validation included examination of 400 dermatology patients’
quiz data at the University of Miami, compared to their diagnostic CPT codes assigned
by a blinded dermatologist who did not have access to the quiz results. The quiz was
able to accurately predict the facial skin diagnosis. Over the years, with adoption of the
quiz by 100 dermatology practices, it has shown to accurately reflect the corresponding
dermatologic diagnosis. All of the validation studies are out of the scope of this article, but
many are listed in the references.
SKIN TYPE CATEGORIZATION COMBINING MULTIPLE PARAMETERS
The BSTI categorizes individuals into 16 distinct skin phenotypes. These are further
subdivided into four sensitive skin subtypes.
The 16-skin type classification is based on four primary parameters or “barriers to skin
health”: dehydration, inflammation, uneven pigmentation, and risk of skin aging (Figure 2).
Each skin type is represented by a combination of these parameters and is assigned to a skin
type octagon that has a corresponding color and number, making it easy for individuals
to remember their skin type. The octagons can be placed on product images, so that the
consumer can shop by skin type, and on product reviews so they will know whose advice is
applicable to their skin type (Figure 3).
Figure 2. The four barriers to skin health are dehydration, inflammation, pigmentation, and aging. An
effective skin care routine should target all relevant barriers rather than just one. The presence or absence of
the barriers in each quadrant represents the skin type visually, as seen in Figure 3.

411 AI-Guided Skin Care
THE PARAMETERS DEFINING BSTS
Oily Versus Dry. Oily skin in the Baumann Skin Typing System (BSTS) is characterized by
sebum production rates of at least 1 mg of sebum per 10 cm2 every 3 hours.23 The occlusive
properties of sebum compensate for an impaired barrier and contain antioxidants.24 In the
BSTS, oily skin is the preferable type. Normal skin falls into this category. The way that
normal, oily, and very oily skin are scored by the BSTI for skin care recommendations is
beyond the scope of this article.
Dry skin has dehydration and a defective barrier, and it lacks sufficient sebum to provide
enough occlusion to overcome this barrier.
A combination skin type is not considered a true skin type in the BSTS. People who self-
identify as combination skin types are one of two possibilities:
• Changing skin type: Some patients experience seasonal variability in their skin type,
with their BST alternating between dry and oily, depending on environmental factors
such as humidity and temperature.
• Oiliness in the T-zone: When there is excessive sebum production in the T-zone and
dryness on the cheeks, the BSTS classifies this as an oily skin type. This is considered
a “normal oily skin type,” and the skin should be treated with a skin care regimen
targeted to oily skin. The moisturizer in the skin care routine is not used in the T-zone
parts of the face that have more sebaceous glands.
Sensitive Versus Resistant. The BSTS divides sensitive skin into four subtypes based on
their propensity to inflammation from different causes. A resistant skin type, on the other
hand, does not have acne, inflammation, or a history of reacting to skincare products. An
individual can be classified as one sensitive subtype or a combination of subtypes.
Figure 3. An illustration of the16-skin type octagons and which barriers to skin health they represent. Note
that skin type 10 has no barriers to skin health. The use of these images is trademarked and cannot be used
without written permission.