Cutometry

A cutometer probe seals against the skin and applies a defined negative pressure, commonly in the range of a few hundred millibar, through an aperture that is typically two millimetres across. An optical system inside the probe measures the skin's vertical displacement during suction and release. The curve is decomposed into total extension, the immediate elastic portion, the slower viscoelastic creep, and the immediate elastic recovery. Ratios of these are reported as parameters such as gross elasticity, net elasticity, and biological elasticity.

Those ratios fall with chronological age and much more sharply with cumulative sun exposure, which is why the sun-exposed dorsal forearm reads differently from the protected volar forearm in the same person on the same day. The measurement is also sensitive to aperture size, applied pressure, site, hydration, and coupling to underlying fat, so protocols fix all of them.

Interpreted as a within-subject change at a fixed site with a fixed device, it is a reasonable mechanical endpoint. Interpreted as an absolute number to be compared across studies, it is close to meaningless. It also cannot attribute change to a structure: collagen network, elastic fibre integrity, ground substance, and water content all influence the same curve.

The trap in cosmetic testing is hydration. Simply moisturising the measurement site shifts the curve toward apparently better elasticity without any change in the dermal matrix, so an unblinded, vehicle-uncontrolled elasticity result mostly measures the moisturiser. A second trap is scale: a change of a few percent in an elasticity ratio can reach statistical significance in a paired design while sitting far below anything an observer or the subject would notice.