Frogs Absorb Water Through Their Skin

Frogs possess a remarkable method of hydration, differing significantly from most other vertebrates. Instead of ingesting water orally, these amphibians draw moisture directly through their skin, a process facilitated by specialized areas on their underside. This "drinking patch," typically found on the belly and inner thighs, is highly vascularized, meaning it contains a dense network (Review) of blood vessels close to the surface. When a frog presses this patch against a damp surface, such as moist soil or a puddle, water is absorbed efficiently into its body.

This unique physiological adaptation relies on osmosis, where water passively moves from an area of higher concentration (the environment) to an area of lower concentration (within the frog's body) across the semi-permeable skin. The frog's skin is uniquely thin, moist, and rich in mucus-producing glands, which are crucial for maintaining its permeability and facilitating both water uptake and gas exchange. This dual function, known as cutaneous respiration, allows frogs to absorb oxygen directly from water or moist air, an essential ability for survival, especially when submerged or during periods of hibernation.

The evolution of such permeable skin has allowed frogs to thrive in diverse environments, from aquatic habitats to drier terrestrial landscapes, by efficiently utilizing available moisture. However, this extraordinary adaptation comes with a significant vulnerability: their permeable skin makes them highly susceptible to environmental pollutants and toxins, which can be absorbed just as readily as water. Consequently, changes in environmental conditions, such as increased droughts due to climate change, pose a serious threat to frog populations by impacting their ability to stay hydrated and perform vital physiological functions.