Amphibians need water for nearly every basic biological function: breathing through their skin, reproducing, developing from larvae into adults, staying hydrated, and regulating body temperature. Unlike reptiles, birds, or mammals, amphibians never fully broke free from water when they evolved to live on land. Their thin, permeable skin and shell-less eggs keep them tied to moist or aquatic environments throughout their lives.
Breathing Through Their Skin
Most amphibians absorb a significant portion of their oxygen directly through their skin, a process called cutaneous respiration. For this to work, the skin must stay moist at all times. Oxygen and carbon dioxide can only cross the skin’s surface by dissolving in a thin layer of water first, then diffusing into the blood vessels just beneath. If the skin dries out, gas exchange slows or stops entirely, and the animal suffocates even if the air around it is perfectly breathable.
This is fundamentally different from how your lungs work. Mammals keep their respiratory surfaces safely inside the body where they stay wet automatically. Amphibians essentially wear their lungs on the outside, which means the surrounding environment has to supply the moisture. Many species do have basic lungs as well, but these are often simple sacs that can’t meet the animal’s full oxygen demand on their own. Some salamanders have no lungs at all and rely entirely on their skin and the lining of their mouth.
A Protective Mucus Layer
To keep their skin functional, amphibians continuously produce mucus from specialized glands. This mucus does far more than just keep things damp. It maintains the skin’s permeability and elasticity, both of which are essential for gas exchange and water absorption. It also serves as a chemical barrier against bacteria and fungi. In tadpoles, a structural protein in the mucus layer creates a coating roughly 6 micrometers thick that helps defend against bacterial infection.
Deeper in the skin, a non-cellular layer made of water-retentive sugar molecules helps slow evaporation. These molecules act like a sponge, holding water close to the skin’s surface. This is especially important for species that bask in the sun, where evaporation would otherwise strip moisture away in minutes. Even with these defenses, though, amphibians lose water through their skin far faster than reptiles or mammals do. Some tropical frogs lose about 0.2% of their body mass per minute through evaporation when they’re not in water.
Reproduction Depends on Moisture
Amphibian eggs lack the hard or leathery shells that protect reptile and bird eggs. Instead, they’re surrounded by a soft, jelly-like coating that provides almost no defense against drying out. Most species lay their eggs directly in water, where the jelly swells and gives the developing embryo a cushion of moisture and nutrients. Without water, these eggs desiccate and die within hours.
Even species that have evolved to breed on land still need high humidity. Some direct-developing frogs in Brazil’s Atlantic Forest and Australia’s Wet Tropics lay eggs in moist leaf litter or soil rather than ponds, but they depend on consistently high moisture levels in those microhabitats. Decreased rainfall in these regions is already predicted to reduce reproductive success because the eggs simply can’t survive in drier soil.
Tadpoles Are Fully Aquatic
Most amphibians spend the first phase of their lives as water-dwelling larvae. Tadpoles breathe through gills, swim with tails, and feed on algae or organic debris in ponds, streams, and temporary pools. They are, for all practical purposes, aquatic animals that later transform into something that can walk on land.
This transformation, metamorphosis, is itself sensitive to water availability. When a pond starts drying up, tadpoles can actually speed up their development. Hormonal changes accelerate the process, pushing them to sprout legs and absorb their tails faster so they can leave the water before it disappears. The tradeoff is real, though: tadpoles that metamorphose early tend to be smaller and sometimes undergo incomplete development, leaving them less fit as adults. Crowding in a shrinking pond also increases predation risk and worsens water quality, compounding the problem.
Drinking Without a Mouth
Amphibians don’t drink water the way you do. Instead, they absorb it directly through their skin, particularly through a specialized region on the belly and inner thighs known as the pelvic patch. This area is specifically designed to maximize water uptake, with skin that is thinner and more permeable than the rest of the body. A frog sitting in a shallow puddle is essentially drinking through its belly.
This system also handles electrolyte balance. Frog skin actively transports salts and regulates acid-base chemistry, playing a role similar to what kidneys do in mammals. Because the skin is so permeable, amphibians are also unusually vulnerable to pollutants and chemicals dissolved in their water sources, which pass through the skin with little resistance.
Cooling Off Costs Water
Amphibians use evaporation from their skin to cool down, much like sweating works in humans. When temperatures rise, water evaporates from the skin surface and carries heat away. This is effective but expensive in terms of water loss. One study on tropical frogs found that the golden poison frog lost water at a rate of about 1 gram per degree Celsius of temperature increase when not submerged. Without access to water to replenish what’s lost, an amphibian can reach lethal dehydration levels surprisingly fast.
Many species manage this by being active only at night or during rain, spending the hottest and driest parts of the day hidden under logs, rocks, or underground. Burrowing both reduces temperature exposure and keeps the animal in contact with moist soil.
How Desert Frogs Survive
A few amphibian species have evolved remarkable workarounds for dry environments, but even these strategies revolve around conserving water rather than eliminating the need for it. Several desert-dwelling frogs in Australia and the American Southwest burrow deep into the soil and enter a dormant state called estivation during dry seasons. As they settle in, they shed layers of skin that harden into a cocoon, sealing in moisture. In some Australian species, this cocoon is a single cell layer thick. In the North American spadefoot toad, it’s a multilayered structure that provides even more protection.
These frogs can remain underground for months, sometimes over a year, waiting for rain. When water finally arrives and soaks into the soil, they emerge, breed explosively in temporary pools, and their offspring race through development before the water vanishes again. It’s a life cycle built entirely around unpredictable access to water.
Why This Makes Amphibians Vulnerable
Because every major life process depends on water or moisture, amphibians are among the most climate-sensitive animals on Earth. A 2023 global assessment published in Nature found that climate change drove 39% of amphibian status deteriorations since 2004, slightly ahead of habitat loss at 37%. Among all threatened amphibian species, 29% face direct threats from climate change effects, alongside 29% threatened by disease, often a fungal pathogen that itself exploits the amphibian’s permeable skin.
The pattern is consistent across continents. In eastern Australia and the western United States, increasing drought frequency and severity are compounding existing threats. Five salamander species in the genus Batrachoseps have declined specifically because of reduced soil humidity and more frequent wildfires. Species living on isolated mountaintops in Venezuela are especially trapped: as suitable moist habitat shifts upward with warming temperatures, there’s simply nowhere higher to go. The researchers behind the assessment noted that given how few studies exist on climate impacts to amphibians, the true scope of the problem is likely worse than current numbers suggest.