The range: 70 to 80 percent, with no long dry spells
The American green tree frog lives in the steamy wetlands and pond margins of the southeastern United States, and in captivity it needs 70 to 80 percent humidity as its normal condition. Brief dips when a door is opened or a lamp runs hot are harmless; what this frog cannot handle is a day in ordinary room air, which in a heated house can sit half the target range. If you are choosing a first amphibian, understand that this number is not a preference to approximate — it is the air the animal's body is built to run on.
Skin that drinks and breathes
A frog's skin is permeable by design. Green tree frogs absorb water directly through the thin skin of their belly and thighs as they sit on wet leaves or in shallow water, and some gas exchange happens through the skin as well. That is why humidity matters more for a frog than for any lizard or snake: dry air does not just irritate, it dehydrates the animal through its largest organ. It is also why everything that touches the frog must be clean — the same permeable skin that drinks water takes in chlorine, soap residues, and lotions from handling hands just as readily.
Water quality is part of the humidity system
Mist with dechlorinated water only — tap water left standing, treated with a reptile-safe conditioner, or spring water — and fill the soaking dish the same way. Chlorine and chloramine in untreated water damage frog skin and the beneficial balance of the enclosure. The dish should be shallow enough for the frog to sit with its head comfortably above the surface; green tree frogs are climbers, not swimmers, and a deep steep-sided bowl is a drowning risk for a tired frog. Change the dish water daily, since the frog will also use it as a toilet.
Holding the range in a glass enclosure
Glass sides, a partially covered screen top, live or silk plants, and a soil or coconut-fibre floor will hold 70 to 80 percent with one or two mistings a day in most homes. Mist in the evening as the frog wakes, wetting the leaves where it hunts and drinks, and again in the morning if the gauge has fallen. A digital hygrometer mounted mid-height, away from the direct spray, keeps you honest. If the number constantly overshoots into saturated fog with condensation streaming down the glass, open more of the top — frogs need humid air that still moves.
When a frog needs more than misting
A green tree frog that stays dark and hunched through the night, refuses food for several nights, or develops cloudy skin, sores, or an unusual bloated look needs an amphibian-aware vet — skin problems in frogs move fast precisely because the skin does so much. Do not wait and mist harder. On ordinary days the rhythm stays light: a glance at the gauge, fresh water in the dish and an evening spray. When a judgement call pops up — shed skin or something worse, a new frog eating too little — put a follow-up question to KinsLe's Kimmy; she answers using the KinsLe Answers library.