The temporary wrinkling of fingers and toes after extended time in water is a familiar phenomenon. This change in skin texture is often dismissed as simple water absorption causing the skin to swell, but this is an outdated explanation. Instead, the appearance of “pruney” skin is a deliberate, active response orchestrated by the body’s own control systems.
The Nervous System Connection
The wrinkling of skin in water is an active process that begins when the skin is exposed to moisture for a sustained period, typically several minutes. This response is controlled by the Autonomic Nervous System (ANS), which regulates involuntary bodily functions. Specifically, the sympathetic branch of the ANS triggers a reaction in the blood vessels located just beneath the skin’s surface.
The active mechanism involves a process called vasoconstriction, which is the narrowing of these small blood vessels in the fingertips and toes. As the vessels constrict, they reduce the volume of the soft tissue—known as the digit pulp—beneath the skin. This reduction in volume causes the attached skin to be pulled inward, forming the characteristic ridges and valleys we recognize as wrinkles.
Scientific observation established this connection in the 1930s when researchers noted that fingers with a severed nerve would not wrinkle when immersed in water. This lack of response proved that the wrinkling was a neurologically mediated action, not a passive soaking effect.
The Biological Reason for Wrinkling
The body’s active decision to wrinkle the skin points toward an evolutionary advantage, which scientists now hypothesize is related to improved dexterity in wet conditions. The pattern of the wrinkles acts much like the tread on a car tire, creating channels that allow water to be efficiently displaced. This drainage system helps to increase the friction between the fingertip and a wet object or surface, thereby improving grip.
Studies have demonstrated this functional benefit by comparing the performance of people with wrinkled fingers to those with unwrinkled fingers when handling submerged items. Participants with wrinkled fingertips were significantly faster at manipulating wet objects, such as marbles or fishing weights, than when their fingers were dry. The wrinkles provided no advantage when handling dry objects, suggesting the adaptation is specifically tuned for wet environments.
This suggests that the feature may have helped human ancestors gather food from wet vegetation or streams, or maintain a more secure footing on wet ground. The rapid and controlled nature of the wrinkling is a temporary adaptation, allowing the skin to return to its normal, smooth state once the need for enhanced wet grip passes.
When the Wrinkling Response Is Concerning
For most people, the temporary appearance of pruney fingers is a normal, healthy, and protective biological response. However, because the process is entirely dependent on a functioning nervous system, a deviation from the normal wrinkling pattern can occasionally signal an underlying health issue. The absence of wrinkling after soaking the fingers for 30 minutes can be a marker for nerve damage, or neuropathy.
Conditions that affect the peripheral nervous system, such as diabetes, can sometimes cause a loss of the wrinkling reflex due to damage to the nerves controlling the vasoconstriction response. Historically, the finger wrinkling test has been used in clinical settings as a simple, non-invasive method to assess sympathetic nerve function.
Conversely, wrinkling that happens too quickly, often within minutes of minimal water contact or even without water exposure, can also be medically relevant. This condition is sometimes referred to as aquagenic wrinkling of the palms and is frequently observed in individuals who have cystic fibrosis or are carriers of the gene. Other factors like severe dehydration, certain circulatory problems, or some medications can cause skin changes that resemble or accelerate the wrinkling response. The normal, temporary response is benign, while a complete lack of response or an inappropriate, rapid one may warrant medical attention.