Iguana Turning Dark or Black: Stress, Temps, or Illness?

Watching your bright green iguana go dark, dusky, or nearly black is unsettling, especially the first time. Take a breath: color change is one of the main ways iguanas communicate with their environment, and the most frequent cause is simply that they are cold. Green iguanas can shift their skin tone deliberately, and a darker body absorbs heat faster. So more often than not, a darkening iguana is telling you something about temperature or mood, not sounding an alarm about disease. That said, a few color patterns do matter, and it is worth knowing which is which.

The key is context. When did the darkening start, how long does it last, and what else is the iguana doing? A dark iguana that is alert, eating, and lightening up under the basking lamp is a very different picture from a dark iguana that is limp, off its food, or showing dry black patches. Let's walk through the likely reasons in order.

Most likely causes

Ranked roughly from most to least common:

• Too cold (thermoregulation). This is the big one. When an iguana is below its preferred temperature, it darkens to soak up more heat. Green iguanas need a basking surface of 95 to 100F and an ambient temperature of 85 to 90F. A cool room, a failed bulb, or a drafty enclosure will push them dark fast.
• Morning warm-up. Many iguanas are darkest first thing in the day and green up as they bask. This is completely normal daily thermoregulation.
• Stress coloration. A new home, recent move, too much handling, a nearby dog or cat, or a reflection they read as a rival can all trigger dark, blotchy stress color. It usually comes and goes with the trigger.
• Dominance or territorial display. A dark chin or dewlap, often with head-bobbing, is a display of dominance or stress rather than illness.
• Shedding. Skin often looks dull, gray, or patchy in the run-up to a shed, which can read as darkening.
• Dehydration. A dehydrated iguana can look dull and dark, usually with sunken eyes and wrinkled skin.
• Illness, including MBD. Metabolic bone disease, caused by poor UVB and low dietary calcium, brings weakness, tremors, and swollen or rubbery jaw and limbs, sometimes alongside persistent dark color.
• Burns or necrosis. Dark, dry, crusty, or leathery patches, especially near a heat source, can be thermal burns or dead tissue. This is localized, not the whole-body darkening of a cold iguana.

What to do tonight

Start with heat, because temperature explains most iguana darkening. Put a digital probe thermometer on the basking surface where your iguana actually sits and confirm it reads 95 to 100F, then check that the ambient enclosure is holding 85 to 90F. Stick-on dial gauges are unreliable, so use a probe. If either number is low, fix the heat before anything else and watch whether the color lightens over the next hour or two as the animal warms.

Check the UVB while you are at it. Iguanas depend on strong UVB to use calcium, and a weak or expired tube is a direct road to metabolic bone disease. Replace UVB bulbs every 6 to 12 months and make sure nothing blocks them. Offer fresh water and a light misting, since a dehydrated iguana looks darker and duller.

Then reduce stress. If the darkening followed a move, new decor, or lots of handling, give the iguana a quiet few days with a secure hide and minimal disturbance and see if the color settles. Look closely at any dark area: whole-body darkening that changes with temperature is behavioral, while a fixed dry crusty patch near the lamp is a possible burn that a vet should see.

Finally, track it, because color that shifts through the day is normal and color that stays dark for days is not. Photograph your iguana at the same time each day, in the same light, and note the temperatures and behavior alongside it. That kind of record turns a vague worry into a clear pattern. With a running health log for your iguana you can store dated photos, weights, and husbandry readings so a trend is obvious, and you can snap a picture to get an AI read on how urgent it looks. VetGPT does this for iguanas and 64+ other species, though it never diagnoses or replaces your vet; it just helps you arrive with facts. If you are still dialing in heat, lighting, and diet, our reptile health tracker covers the husbandry that prevents most of these color scares.

Common Questions

Why is my iguana turning dark?

Usually temperature. Green iguanas darken to absorb more heat when they are too cold, so a dark iguana often means the basking spot or ambient temperature is below target. Aim for a basking surface of 95 to 100F and an ambient of 85 to 90F. Stress, morning warm-up, shedding, and dominance displays can darken them too, and the color typically returns to green once the animal is warm, calm, and left alone.

Is it normal for my iguana to be dark in the morning?

Yes. Plenty of iguanas wake up dark and green up as they bask, because darker skin heats faster. A cool-morning iguana that looks nearly black at sunrise and brightens under the lamp is doing exactly what it should. Only worry if it stays dark all day despite correct temperatures, or if other symptoms appear.

Can stress make an iguana turn black?

It can. New surroundings, frequent handling, a nearby pet, or a perceived rival can all bring on dark, blotchy stress color, and a dark chin or dewlap is often a dominance or stress display. Stress darkening comes and goes with the trigger, so removing the stressor and providing steady heat and a secure hide usually settles it within a few days.

When should I worry about my iguana's dark color?

Call an exotic vet if the darkening is persistent and paired with lethargy, if the jaw or limbs look swollen or rubbery, which can point to metabolic bone disease, if the iguana is refusing food, or if you see dark, dry, crusty patches that look like burns or dead tissue. Those are not simple thermoregulation and need hands-on evaluation.