Melissa Kaplan's
Herp Care Collection
Last updated January 1, 2014

Blackening Skin, Blackening Skin Syndrome, and Vesicular Dermatitis

©1996, 2000 Melissa Kaplan


Black Skin
There are four reasons why your iguanas skin may turn black. All of them are red flags to you that something is wrong with your iguana and that action needs to be taken.

It must be noted that there are some iguanas from some areas across their range (or variants within populations) whose normal coloring is a brown/tan ground with yellow/green markings. These iguanas are this color from the time they emerge from the egg. They are never what we consider normally colored (green with dark stripes and/or patches). If your iguana started out green and then turned black, it is not a normal color shift - it is a sign that you need to get in there and do something to fix the iguana or its environment.


Blackening Skin
An iguana who is under severe stress will slowly turn from green to dark brown, then black. The color change will start first on its body and head, extending down its tail, legs and belly. The belly and sides may first go from green to yellow before finally going brown and black.

This type of color change is often due to psychosocial stress, such as when an iguana is housed with another iguana or more than one iguana who is intimidating it. The iguana whose color changes is the subordinate iguana and, if you watch carefully, you will see that it is being kept out of the basking areas, away from food (or from getting enough food) and is often to be seen at the bottom of a pile of basking iguanas.

Aggression does not need to be overtly physical. Iguanas (and other animals) can signal their dominance and warnings to others of their species by seemingly insignificant (to unknowing humans) postural changes: a shift in head position, a slight flare of the dewlap, a minor lateral compression of the body. Any one of these signals are enough to warn a subordinate iguana away from whatever it is the dominant iguana doesn't want the subordinate doing.

If this happens to your iguana, you must separate it from the dominant iguanas and house it alone or with one iguana with whom it is fully compatible. If you do not the iguana will either starve to death slowly from inadequate food intake or chronic hypothermia, or will develop metabolic bone disease from inadequate access to UVB lighting...assuming it doesn't develop a serious systemic infection which ultimately may kill it.

Iguanas who do not like certain people or situations will also turn dark brown or black when subjected to those people or situations. One way to tell if it is a temporary stress situation like that is to have the iguana held by someone it likes and is comfortable with, and have that person hold and pet the iguana. If the iguana begins to change back to its normal color within a minute or so, and then turns brown/black again within minutes of being placed back with the other person or into the stressing situation, you will have pinpointed the stressor. (Note: This is consistent enough that I have used this rapid stress-related color change indicator as a determinant when deciding to adopt out an iguana to an individual. If the iguana repeatedly turns black when held by or sits on the prospective adoptor, but turns rapidly green again when held by me or another person, I will not adopt that iguana out to the prospective adoptor, no matter how good I think that person will be with that, or any other iguana. Instead, I will try to find an iguana who is comfortable with that person.)


Burns from heat sources, either overhead lights or undertank/substrate pads can cause thermal burns. Sometimes they are first seen as a fluid filled blister or cluster of blisters, or as a darkening or blackened patch of skin. Please see the article on burns to find out how to treat them.


Blackening Skin Syndrome
Blackening skin syndrome is a sort of nonspecific name for a skin condition that may have one of many causes. The condition itself may range from relatively benign (corrected by proper diet, heat, and environment) to serious (advanced skin and systemic infections).

An all-over black and crusty skin may be found on iguanas who have been housed in filthy or otherwise inappropriate conditions (too cold, overcrowded, filthy). Once such an iguana is housed and fed properly, and soaked daily in warm povidone-iodine/water baths, the first shed can be startling, with the black scabby skin splitting apart to reveal the new, brilliant green skin below.

Iguanas housed in overcrowded and inappropriately outfitted tanks do not have a chance recover from similar conditions experienced during import and trade. Their skin gets scratched and bitten by other iguanas and, left as they are in generally dirty enclosures with little access to proper heat or food, the wounds heal little if at all. The result is an iguana webbed in crusty scabs, often thin and lethargic. Proper diet, care, and daily povidone-iodine/water baths will help the wounds heal. The scabs will fall off to be replaced by gray scars or green scales.

Heavy infestations of mites may lead to areas of crusty, scabby, or weepy areas on the body, especially where the scales are smaller and thinner: around the head, neck, dewlap and armpits. In severe infestations, such crusting may be found along the dorsal crest as well, in addition to anywhere there are any scratches or abscesses in the skin. Mites are most active at night, and if they are the black reptile mites (as opposed to the bright red-orange chigger mites), they may not be seen if the owner is not alert in looking for them. The mites are blood-sucking parasites who congregate where the blood is easiest to get to. Given enough of them, they can literally chew through the skin in large enough areas to create large scabs or crusty infections. As with other types of infections and conditions, both the environment and the reptile must be treated (see Getting Rid of Reptile Mites).

If not caught in time, or not treated properly, the infection may spread to the blood and organs and result in the iguana's death. While blackening skin syndrome is not automatically fatal as it is sometimes claimed to be, if you fail to act on it, and fail to correct the underlying conditions, it will be. See Vesicular Dermatitis below for similar conditions.


Vesicular Dermatitis
Vesicular dermatitis, sometimes called blister disease, scale rot, or necrotizing dermatitis, is commonly caused by housing reptiles in moist, dirty environments. As the animal is forced to lie on damp substrate saturated with rotting food or feces and urates, the skin becomes infected. Watery blisters are the first sign. The infection may pass into the body causing septicemia (infection of the blood) and passing to internal organs. In small reptiles, or reptiles already severely weakened from illness, environmental or psychological stresses, infection may be rapid, and rapidly fatal. The skin may rot away from the initial blister, leaving the body more susceptible to bacterial and fungal invasion and thermal burns.

As with many illnesses and conditions, treatment must be two-fold. The iguana must be seen by a vet for evaluation and initiation of treatment (antibiotic therapy, debriding necrotic skin and tissue), and the iguana's environment must be thoroughly cleaned, disinfected, and set up properly to promote healing and growth, not disease.

When small blisters are first noticed, the iguana may be soaked in a povidone-iodine (Betadine®) and water bath one or two times daily, followed by a dab of triple-antibiotic ointment. During recovery, the substrate should be unprinted paper (newsprint, paper towels, butcher paper), clean terry cloth towels, or plain linoleum. All bottom heat should be suspended during this period, with the necessary thermal gradients being provided by overhead radiant heat sources. If the blisters do not resolve in a few days, or if they are large blisters or are spread out over a wide area, the iguana should be seen by a vet immediately.

Small blisters, crusting, or ulceration of the skin may also be caused by exposure to toxic substances, such as residues from cleaning compounds and disinfectants, and from toxic substrates such as cedar wood chips or shavings. The blisters or inflammation should be treated as above and the enclosure thoroughly cleaned out of all residues. If the condition is the result of toxic substrates, the material not only needs to be removed and discarded, but the inside surfaces of the enclosure must be washed out with hot soapy water to remove all residues from the oils in the substrate. After thorough rinsing and disinfection, the enclosure may be outfitted with a proper substrate for the duration of the healing period.

Crusty blisters or oozing bumps may also be a form of topical Salmonella. If you can discern no external causes for the blistering or bumps, such as toxic substrates, thermal burns or moist, dirty environments, and a few days of topical antibiotic or antifungal medications do not result in visible signs of healing, your iguana should be seen by a vet for evaluation and proper treatment.



Boyer, T.H. (1991) Common Problems and Treatment of Green Iguanas. Bulletin of the ARAV 1(1):8.

De Vosjoli, P. (1992) The Green Iguana Manual. Advanced Vivarium Systems, Lakeside CA.

Frye, F. L. (1991) Reptile Care: An Atlas of Diseases and Treatments. Neptune City NJ: T.F.H. Publications, Inc.

Mader, Douglas, (Ed.). (1996) Reptile Medicine and Surgery. WB Saunders, Company, Philadelphia PA.

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