Determining Skin Type
— Sebum, TEWL, and Barrier as Key Indicators
Dry, oily, or combination skin? Distinguishing between your constitutional skin type and transient conditions allows for more reliable skincare decisions. A physiological classification.
"Dry skin," "oily skin," "combination skin" — these categories sound familiar, but in practice, they are often misleading. Determining your skin type based on a single observation or an online questionnaire leads to skincare decisions based on shaky foundations. Dermatology, by contrast, uses systematic methods that differentiate between a genetically determined skin type, a daily skin status, and reactive conditions.
To complicate matters, many people assess their skin in a permanently altered state — following over-cleansing, seasonal dehydration, or after using barrier-weakening active ingredients. What appears in the mirror is not a stable skin type, but a momentary snapshot under external stress. This article explains how dehydrated skin can be distinguished from constitutionally dry skin — and why this is crucial for shaping your routine.
Sebum, TEWL, and barrier status: What differentiates skin types physiologically
Skin type is not an opinion, but a function of measurable parameters: sebum production rate (sebometry), transepidermal water loss (TEWL), and stratum corneum hydration. Each of these values follows its own genetic baseline — overlaid by age, hormone levels, environmental factors, and skincare habits. A sebometer measures oil content at defined points on the face; a tewameter quantifies how much water the skin evaporates per unit of time. These instruments are only available in clinical settings — but their logic can be applied to everyday observations.
Sebaceous glands respond to androgenic hormones and are stimulated by the growth factor IGF-1. High activity (seborrhea) produces the characteristic midday shine and enlarged pores. Sebostasis — insufficient sebum production — leads to flaking, a feeling of tightness, and increased sensitivity. Both extremes are constitutionally influenced but can be shifted by external factors.
TEWL measures the passive diffusion of water through the epidermis. When the barrier is intact — composed of ceramides, free fatty acids, and cholesterol — this value remains low. If the barrier is compromised by detergents, air conditioning, or harsh active ingredients, TEWL increases measurably. High TEWL is not a skin type characteristic, but a sign of barrier stress — an important distinction for skincare.
The Natural Moisturizing Factor (NMF) — a mixture of amino acids, urea, lactic acid, and salts — keeps the horny layer supple. Those who wash away NMF-containing components by over-cleansing or break them down through aggressive exfoliation experience transient water deficiency, which mimics constitutionally dry skin. Corneometer measurements show such differences within hours.
Four types, countless conditions: How true constitution and reactive phases overlap
To determine your skin type, you first need a "zero line": 24–72 hours without active ingredients, using only a mild cleanser and no new products. Only within this stabilized window can the skin’s constitutional sebum-water ratio be identified — rather than one created by external interventions. Chronobiological rhythms also influence when measurements are particularly meaningful throughout the day.
From observation test to routine decision: What really helps
- Maintain a 72-hour stabilization window before the self-test (only mild cleansing, no active ingredients)
- Observe over several days and at different times of day, not based on a single snapshot
- Differentiate between oil film (sebum) and feeling of tightness (TEWL) — both can occur simultaneously
- Determining skin type immediately after exfoliation, sauna, or travel — barrier stress distorts the picture
- Online questionnaires that ignore season, climate, and current routine
- Products for "oily skin" used for reactive shine — aggressive matting can increase seborrhea
The Porcelain Skin Serum accompanies the day with pullulan, two forms of hyaluronic acid, kigelia extract with bioactive flavonoids, amino-acid-based actives, functional silk polypeptides, and licorice root extract — ingredients focused on moisture retention, barrier function, and skin structure, regardless of which constitutional skin type the skin is assigned to. For the night, the Blue Crystal Drops facial oil complements this with bioactive phytosterols, Vitamin C, bisabolol, and essential oils of blue lotus and blue tansy — a protective film that supports the nocturnal regeneration phase. The rhythm logic behind this, describing why day and night care fulfill physiologically different requirements, is detailed by Chrono-Barrier Skin Science™.
For specific skin concerns — such as persistent irritation, lasting feelings of tightness, or unclear changes in skin appearance — a professional medical assessment should be sought.
Frequently asked questions
Can my skin type change over the course of my life?
Yes. Sebum production tends to decrease with age, especially in women after menopause. Hormonal phases like pregnancy or pubertal androgen spikes also permanently alter seborrheic status. What changes less, however, is the genetic disposition for ceramide synthesis — which is why constitutionally dry skin generally remains dry, even if it appears well-tolerated during certain phases.
What is the difference between dry and dehydrated skin?
Dry skin describes a constitutional state with genetically lower sebum production and often restricted lipid barrier. Dehydrated skin, on the other hand, is a transient state of water loss that can affect any skin type — even oily skin. Dehydration is often visible through fine lines during movement, a feeling of tightness, and a matte, dull complexion, while sebum production can simultaneously be normal or increased. More on this in the article on hydrating skincare 2026.
Is the classic tissue test for skin types reliable?
Only to a limited extent. The test — cleansing facial skin, waiting an hour, pressing a paper tissue onto the T-zone and cheeks, and reading the oil film — can provide a rough classification, but it can be distorted by numerous variables: room temperature, humidity, the cleanser used, and the time of day significantly influence the result. As an orientation in a stabilized state (after 72 hours without active products), it has some value, but it does not replace dermatological sebometry.
Why does my skin look different in the morning than in the evening?
Sebum production, TEWL, and hydration are subject to circadian fluctuations. In literature, sebum secretion often reaches its maximum at midday; TEWL values can be higher in the evening than in the morning. Simultaneously, the skin barrier regenerates preferentially during nighttime hours. This rhythm is the core of Chrono-Barrier Skin Science™ and explains why day and night care should be oriented differently.
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- Darlenski R. & Fluhr J.W. (2018). Influence of skin type, race, sex, and anatomic location on epidermal barrier function. Clinics in Dermatology, 36(3), 314–321.
- Zouboulis C.C. et al. (2014). Sebaceous gland carcinoma. Journal of the American Academy of Dermatology, 70(5), e1–e17. [Background information on sebum physiology]
- Elias P.M. (2005). Stratum corneum defensive functions: an integrated view. Journal of Investigative Dermatology, 125(2), 183–200.
- Yosipovitch G. et al. (2021). Circadian and seasonal variations in skin barrier function. British Journal of Dermatology, 185(3), 507–516.
This article is for informational purposes only and does not constitute medical advice. For specific skin concerns, we recommend consulting a board-certified dermatologist.
