We have all experienced the familiar sight of our fingertips wrinkling after a long soak in the bath or a swim. This common phenomenon, often referred to as “pruney fingers,” is a temporary change in our skin’s appearance. What exactly causes this transformation?
The Water Absorption Theory
For a long time, it was thought that wrinkled fingertips resulted from the skin simply absorbing water and swelling. The outermost layer of our skin, the stratum corneum, does absorb some water when exposed to moisture. This absorption can cause the skin’s surface area to increase. This theory suggested that because this outer layer is tightly attached to the underlying living tissue, it compensated for the increased surface area by wrinkling. However, this explanation alone does not fully account for the observed wrinkling, as not all skin on the body wrinkles similarly, and fingers would swell rather than shrivel if it were purely water absorption.
The Nervous System’s Role
The current understanding points to an active biological response controlled by the nervous system. Rather than being a passive process of water absorption, fingertip wrinkling is primarily regulated by the autonomic nervous system, specifically its sympathetic division.
When fingers are submerged in water, nerve signals trigger vasoconstriction, where blood vessels beneath the skin in the fingertips narrow. This constriction reduces blood volume in the finger pads, causing the underlying tissue to shrink. As the skin on the surface is tethered to these shrinking structures, it shrivels and forms the characteristic wrinkles. This mechanism is supported by observations that individuals with nerve damage in their hands often do not experience water-induced wrinkling or have a significantly reduced effect.
The Purpose of Wrinkled Fingertips
Scientists propose that this controlled wrinkling serves a functional purpose, likely an evolutionary adaptation to improve grip in wet conditions. The wrinkles act similarly to car tire treads, creating channels that help displace water from the contact surface. This improves friction and a more secure hold on wet objects.
Studies have demonstrated that individuals with wrinkled fingers can handle wet objects more efficiently and quickly than those with unwrinkled fingers. Our fingers are not permanently wrinkled likely due to the trade-off of reduced sensitivity that would occur if they were constantly in this state.
When Wrinkling Indicates a Problem
While water-induced wrinkling is typically a normal and temporary occurrence, persistent or unexplained wrinkling, particularly when not associated with water exposure, could signal an underlying health issue.
Several conditions can cause non-water-related wrinkling:
- Dehydration, which can cause the skin to lose elasticity and appear shriveled.
- Nervous system conditions, such as peripheral nerve damage, which can alter or prevent the normal wrinkling response. A “wrinkle test” is sometimes used by medical professionals to assess nerve function.
- Circulatory problems, like Raynaud’s phenomenon, involving the constriction of blood vessels in response to cold or stress.
- Conditions such as diabetes, which can affect sweat glands and lead to dry skin, or thyroid disorders, impacting metabolism and temperature regulation.
- Aquagenic Wrinkling of the Palms (AWP), a rare condition causing exaggerated and rapid wrinkling, often accompanied by discomfort, and associated with cystic fibrosis.
If unusual or persistent wrinkling occurs without water exposure, especially if accompanied by other symptoms, it warrants consultation with a medical professional.