Clinical Glossary
A reference index for dermatological mechanisms, formulation chemistry, and active compounds.
A
- Acid Mantle
- The fine film on the surface of the skin, composed of sebum, sweat, and dead skin cells. It is naturally acidic (pH 4.5 - 5.5) which inhibits the growth of pathogens. Disrupting this with alkaline cleansers (true soap, pH 9+) compromises barrier function.
- AHA (Alpha Hydroxy Acid)
- Water-soluble carboxylic acids (Glycolic, Lactic, Mandelic) that exfoliate by decreasing calcium ion concentration in the epidermis, disrupting cellular adhesion (desmosomes). Require a pH of 3.0-4.0 for efficacy.
B
- BHA (Beta Hydroxy Acid)
- Lipid-soluble chemical exfoliant (Salicylic Acid). Unlike AHAs, BHAs can penetrate sebum within the follicle, making them effective for treating comedonal acne.
C
- Ceramides
- Waxy lipid molecules (sphingolipids) that make up 50% of the stratum corneum's lipid matrix. They act as the "mortar" between cellular "bricks", preventing moisture loss and blocking environmental irritants.
P
- pKa (Acid Dissociation Constant)
- The pH value at which a chemical species will accept or yield a proton. In skincare, if a product's pH is equal to the acid's pKa, it means 50% of the acid is in its active "free" form, and 50% is ionized (inactive salt). If pH > pKa, efficacy drastically drops.
T
- TEWL (Transepidermal Water Loss)
- The continuous, passive evaporation of water from the dermis through the epidermis to the atmosphere. Increased TEWL is a primary indicator of a compromised skin barrier.