Corneometry

Corneometry is a non-invasive analytical technique used to assess the water content of the stratum corneum, the outermost layer of the skin. The method relies on measuring the dielectric properties of the skin with a probe, most commonly via capacitance-based devices known as corneometers. In these instruments, the water content of the stratum corneum alters the dielectric constant of the tissue, which changes the electrical capacitance read by the probe. The result is typically expressed in arbitrary units that correlate with skin hydration levels.

Standard practice involves placing the probe on a clean, moisturization-free area (commonly the volar forearm or cheek) under controlled environmental conditions. Readings are taken after a short equilibration period to minimize the influence of surface moisture or occlusion. Multiple measurements are often averaged to improve reliability, with careful attention to consistent probe pressure and avoiding repeated probing at the exact same micro-site.

Corneometry is widely used in dermatology, cosmetic science, and pharmaceutical development to evaluate skin hydration and the moisturizing performance of products. It is commonly paired with other metrics such as transepidermal water loss (TEWL) and sebum measurements to provide a fuller hydration profile. The technique is valued for its rapid, non-destructive readings on living skin, but results can be influenced by environmental conditions and surface contaminants.

Limitations include that corneometry mainly reflects surface hydration and may not reflect deeper skin water content. Readings can vary with temperature, humidity, recent washing, cosmetics, or skin oils. Inter-device variability and the need for standardized calibration protocols should be considered when comparing results across studies or instruments.

The technique became widely adopted in the late 20th century with commercial corneometers used in research and product testing.