TL;DR: MBD (metabolic bone disease) is a softening and weakening of the bones and jaw caused by a lack of calcium and/or vitamin D3. In pet iguanas it is the most common cause of death, and it is almost entirely preventable. The root cause is nearly always hidden in three things owners tend to underestimate: enclosure temperature, UV-B exposure, and dietary calcium. An iguana can look "just fine" while its bones quietly soften, and by the time the jaw feels rubbery or the legs go weak, the damage is usually advanced. The good news is that correcting temperature, UV-B, and diet early prevents or slows many cases. If you see a soft jaw, weak legs, tremors, or an iguana that stops eating, this is not something to wait out at home, your iguana needs an exotic vet.
Your iguana looks healthy. Good colour, still climbing, still eating. Yet behind that, one disease can develop slowly with no obvious symptoms, until suddenly it is too late. That disease is MBD (metabolic bone disease), and it is the most common reason pet iguanas die young in Indonesia.
What makes MBD dangerous is how it works: quietly and gradually. Iguanas hide illness, so you may only notice a problem once the jaw already feels soft, the legs have weakened, or the animal starts seizing. By then, bone damage is usually well underway. The irony is that MBD is almost entirely preventable, because its cause is not a virus or bad luck, but three things within your control: temperature, UV-B, and calcium.
This article explains why iguanas are so prone to MBD, the chain that connects temperature and UV-B to healthy bone, the signs you should recognise early, what you can do at home, and when you should call a Prabasa vet. Disclaimer: this is general guidance based on reptile husbandry and exotic medicine principles, not a substitute for a direct exam by an exotic vet for your iguana's specific condition.
What MBD is and why iguanas are most at risk
MBD is a broad term for a group of bone disorders. The most common one in iguanas is the condition where the body lacks usable calcium, so it pulls calcium out of the bones to meet other needs. As a result the bones and jaw soften, bend easily, and fracture easily. In advanced cases the muscles and nerves are affected too, because calcium is essential for both.
Why are iguanas among the most frequently affected? A few reasons:
- Green iguanas are strict herbivores that depend entirely on plants for calcium. If the diet is wrong (too little calcium, or too much of what blocks calcium absorption), their calcium reserves deplete fast.
- Iguanas need UV-B to make their own vitamin D3. Without enough D3, calcium from food cannot be absorbed well, no matter how good the diet is.
- Iguanas grow fast when young. Babies and juveniles build bone rapidly, so their calcium demand is high and deficiency causes damage sooner.
- Many are kept indoors with enclosures short on sunlight and with UV-B lighting that is inadequate or already weak, two things owners often fail to notice.
In other words, MBD in iguanas is rarely caused by one big mistake. It usually results from a combination of small shortfalls that pile up: slightly too little UV-B, slightly too little calcium, less-than-ideal temperatures, over many months.
The chain of causes: temperature, UV-B, and calcium
To prevent MBD, you need to understand how the three connect. Here is the simple chain: correct temperature keeps the iguana active and warm enough to digest and use its nutrients, UV-B lets its body make vitamin D3, and that vitamin D3 is what lets calcium from food actually be absorbed and used for bone. Break one link and the rest fail with it.
Temperature: the fuel for the whole system
Iguanas are ectotherms, meaning their body temperature follows the environment. They regulate heat by moving between warm and shaded areas, so the enclosure needs a clear temperature gradient, not one flat temperature. As a commonly used general guide:
- A daytime basking spot around 32 to 35 degrees Celsius.
- A daytime ambient temperature (most of the enclosure) around 27 to 30 degrees Celsius.
- A cooler shaded area for the iguana to cool down.
- A nighttime drop, while still kept from getting too cold.
Why does this matter for MBD? A cold iguana becomes sluggish, eats less, and digests more slowly, so nutrient absorption including calcium suffers too. Chronically low temperatures weaken the entire system. Use a digital thermometer at a minimum of two points (basking and ambient), and do not guess temperature by hand.
UV-B: the key to vitamin D3 that is so often forgotten
This is the part most often behind MBD. Iguanas need UV-B light to convert a compound in their skin into active vitamin D3. Without enough D3, most of the calcium from food is wasted rather than absorbed. A few things to understand:
- A dedicated reptile UV-B lamp is mandatory for an indoor iguana. Ordinary room lighting, a general UV/blacklight, or a heat lamp alone do not emit proper UV-B.
- Glass and plastic block UV-B. There should be no glass or acrylic barrier between the lamp and the iguana, and do not rely on sunlight coming through a closed window.
- UV-B lamps weaken over time. UV-B output drops long before the lamp visibly dies, so it needs periodic replacement even while it still glows brightly. An old lamp that is "still on" is a common trap that slowly starves the iguana of D3.
- Distance and duration matter. A lamp mounted too far from the basking spot becomes almost useless, and iguanas need a regular daily light-dark cycle.
- Direct sunlight is the best UV-B source. Basking under the sun (with no glass barrier) is far stronger than any lamp. But never leave an iguana outside unattended, because overheating, escape, and predators are real risks.
Calcium and diet: the raw material has to be there
Temperature and UV-B are useless if there is no calcium to absorb. Green iguanas are strict herbivores, so all of their calcium comes from plants. The basics:
- Base the diet on a variety of dark leafy greens that are high in calcium, with variety, not just one type.
- Watch out for foods that block calcium. Some vegetables are high in oxalate (for example spinach in excess), which binds calcium and makes it hard to absorb. This is often missed: the iguana "is getting greens" but its calcium still is not being absorbed.
- Avoid animal protein. Adult iguanas are not built to digest meat, fish, eggs, or insects, and feeding it strains the kidneys over the long term.
- Calcium supplementation is often needed, especially for fast-growing babies and juveniles. The form, type, and how often to supplement are best decided together with an exotic vet, because each iguana's needs differ with age, diet, and UV-B setup. Over-supplementing can also be harmful, so this is not something to guess at on your own.
Signs of MBD you should recognise
MBD develops gradually, so its early signs are subtle and easy to miss. The sooner you catch it, the better the chances of correcting it.
Early signs that are often missed
- A slow decline in appetite, or becoming a picky eater.
- Less activity, staying still more, climbing rarely.
- Stunted growth in a baby or juvenile compared to what is expected.
- A changing gait, stiff-looking steps, or legs that seem to drag.
More obvious and more serious signs
- A lower jaw that feels soft or rubbery when gently touched. A healthy jaw feels hard like normal bone. A "rubbery" jaw is a classic MBD sign.
- Swelling of the jaw or of the leg bones (long bones looking thickened).
- Weak legs, difficulty supporting the body, or walking with a dragging motion.
- Bent bones or fractures that appear without serious injury.
- Tremors, twitching muscles, or seizures, which can indicate a sharp drop in blood calcium.
- Paralysis of a limb in severe cases.
- Severe lethargy and refusing to eat.
Signs such as a soft jaw, weak legs, tremors, or seizures point to fairly advanced MBD and count as a situation that needs prompt care, not something to wait out at home.
What you can do at home
Most MBD prevention happens at home, long before an iguana needs a vet. The focus is closing the gaps in temperature, UV-B, and calcium. Here is what you can do yourself:
- Audit your UV-B today. Check whether the lamp you use is genuinely a dedicated reptile UV-B lamp, not just a bright or heat lamp. Remember when it was last replaced. If it has been a long time or you cannot recall, it is a strong candidate for the problem.
- Remove UV-B barriers. Make sure there is no glass or plastic between the lamp and the iguana, and that the lamp is not mounted too far from the basking spot.
- Measure temperature with a thermometer, not a guess. Place a thermometer at the basking spot and in the ambient area, then adjust so there is a clear warm-to-cool gradient.
- Shift the diet toward varied dark leafy greens, and reduce or stop animal protein and excessive high-oxalate foods.
- Use direct sunlight safely. Where possible, give basking time under the sun with no glass barrier, under full supervision and with access to shade and water.
- Keep the iguana hydrated. Provide clean water, maintain enclosure humidity, and offer fresh, water-rich greens.
- Weigh and observe regularly. Track body weight and watch appetite, activity, and gait. Weight loss and changes in activity are often the earliest alarms.
Important: home steps are meant to prevent and stabilise the environment, not to treat MBD that has already set in. If you already see a soft jaw, weak legs, or tremors, fixing the lamp and diet alone is not fast enough to save the situation, this needs a vet's assessment. And please do not give medication, calcium injections, or high-dose supplements on your own initiative, because the wrong dose in a reptile can be dangerous.
When you should call a vet
Contact an exotics-experienced vet promptly if you notice any of the following in your iguana:
- A lower jaw that feels soft, rubbery, or swollen.
- Weak legs, difficulty walking, or apparent paralysis.
- Tremors, twitching muscles, or seizures.
- Bent or fractured bones without serious injury.
- Not eating for more than a few days, especially in a baby or juvenile.
- Severe lethargy, eyes often closed, and unwillingness to move.
- A newly obtained iguana (especially wild-caught) that has not been checked should have an initial exam in the first months.
At the clinic or during a visit, the vet can assess bone condition, check calcium status, correct the diet and environment setup, and provide appropriate medical treatment if MBD is present. Early MBD has a far better outlook than advanced MBD, so it is better to get checked early than to wait for things to worsen.
Note that many medications and treatments for dogs or cats are not safe for reptiles, and iguanas need a vet versed in exotic medicine. For an adult iguana with a large enclosure, transporting the animal to a clinic can be very difficult and add stress, so a house-call vet for iguanas is often the more practical choice. The vet can also see your enclosure setup, temperature, and UV-B lamp firsthand and give relevant husbandry advice.
Consult a Prabasa vet
If you are unsure whether your iguana is showing signs of MBD, or you want to confirm your temperature and UV-B setup is right before problems appear, you do not have to guess. You can start with an online consultation with a vet for an initial chat and guidance, or schedule a house-call visit if the iguana needs a direct exam.
Need a consultation about your iguana? Reach us on WhatsApp, tell us your iguana's age and size, the enclosure setup (UV-B lamp and temperature), the condition you are worried about, and your area. Our team will help point you to a partner vet experienced with reptiles.
FAQ
My iguana still eats and seems active, could it still have MBD?
Yes. MBD develops gradually, and iguanas hide illness. In the early stage, an iguana often still eats and moves even as its bones begin to run short on calcium. So do not wait for the iguana to look "clearly sick". Prevention through correct temperature, UV-B, and diet from the start is by far the most powerful approach.
Is a heat lamp alone enough to prevent MBD?
No. A heat lamp regulates temperature, but it does not emit proper UV-B. Iguanas need both: a heat source for basking and a dedicated reptile UV-B lamp to make vitamin D3. Without adequate UV-B (or direct sunlight), calcium from food will not be absorbed well.
My iguana's jaw feels a bit soft, can it still get better?
A jaw that feels soft is an MBD sign to take seriously, not to wait out. Many cases treated earlier have a better chance of improvement, but this needs an exotic vet's assessment to determine how far the condition has gone and the safe steps to correct it. Do not try to treat it yourself with high-dose supplements.
How often do I need to replace the UV-B lamp?
UV-B output declines with use, long before the lamp visibly dies, so the lamp needs periodic replacement even while it still glows brightly. The exact interval differs between products, so follow the guidance for the product you use and note the installation date. An old lamp that is "still on" is a common hidden cause in MBD cases.
Does Prabasa Vet offer consultations and visits for iguanas?
Yes. Adult iguanas with large enclosures benefit greatly from a home visit, because transport to a clinic is difficult and adds stress. When you contact us on WhatsApp, mention your iguana's age and size, the enclosure setup (UV-B lamp, temperature), the condition you are worried about, and your area. Our team will help point you to a partner vet experienced with reptiles.
Wrapping up
MBD sounds frightening, and it is dangerous, but there is one reassuring fact: this disease is almost entirely within your control. It is not a virus or fate, but the result of temperature, UV-B, and calcium gaps that pile up over time. With the right UV-B lamp replaced on time, a measured temperature gradient, a diet based on dark leafy greens, and the habit of observing your iguana every day, most MBD cases can be prevented entirely.
If you already see an early sign, or simply want to be sure your setup is right, getting checked early is always better than waiting. An iguana cared for with proper husbandry can live a long and healthy life, and today's preventive steps decide that.
See also: Keeping a Green Iguana: Enclosure, Herbivore Diet, and UV-B, Reptile Care for Beginners: Temperature, UV-B, and Diet, House-Call Vet for Iguanas, House-Call Exotic Vet.
Medical references used in this article
This article draws on reptile husbandry and exotic medicine principles from the following sources:
- Girling SJ, Raiti P (eds). BSAVA Manual of Reptiles, herbivorous lizard husbandry, metabolic bone disease prevention and therapy, UV-B and temperature requirements
- Mader DR, Divers SJ (eds). Mader's Reptile and Amphibian Medicine and Surgery. Elsevier, pathophysiology of MBD/hypocalcaemia, common diseases of captive iguanas
- ARAV (Association of Reptile and Amphibian Veterinarians), green iguana husbandry guidance, UV-B protocols, early MBD detection
- LafeberVet exotic pet care references, iguana herbivore diet and enclosure temperature gradients
This is general guidance. For your iguana's specific condition, especially a soft jaw, weak legs, tremors, or refusal to eat, consulting an exotic vet is the right step.
