Yellow Fungus Disease (Fungal Dermatitis) in Leopard Geckos

Yellow fungus disease is a common name pet parents use for a serious fungal skin infection seen in lizards. In reptiles, this syndrome is often associated with Nannizziopsis fungi, which can cause thickened, crusty, discolored skin lesions and may become aggressive if not treated early. In some lizards, the lesions are yellow, but they can also look tan, brown, gray, or dark and scabby.

In leopard geckos, fungal dermatitis can be easy to miss at first. A small rough patch may look like retained shed, a minor burn, or a healing scrape. Over time, the skin may thicken, crack, peel, bleed, or spread to nearby areas. Some geckos also become less active, eat poorly, lose weight, or seem painful when handled.

This is not a condition to monitor at home for long. Reptile fungal skin disease can worsen beneath the surface, and secondary bacterial infection may develop in damaged skin. Because several skin problems can look similar, your vet will need to sort out whether the lesion is fungal, bacterial, traumatic, related to shedding, or caused by another underlying problem.

The good news is that some leopard geckos do improve with early diagnosis, antifungal treatment, and better husbandry. The outlook is usually better when lesions are small, the gecko is still eating, and the infection has not spread deeply.

The exact source of infection is not always obvious, but reptile yellow fungus disease is commonly associated with Nannizziopsis fungi. These organisms are considered contagious in reptile collections, and many cases are reported in animals that were recently acquired or had contact with other reptiles through breeders, pet stores, shared equipment, or temporary housing.

Skin damage often seems to give infection an opening. Minor trauma, retained shed, burns from overheated surfaces, rubbing injuries, or chronic irritation from poor enclosure conditions may make it easier for fungi to invade. Once the skin barrier is damaged, secondary bacterial infection can also develop and make lesions look worse.

Stress and husbandry problems may increase risk. For leopard geckos, that can include poor sanitation, overcrowding, chronic dampness, dirty hides, unclean decor, or an enclosure that stays too humid overall. Leopard geckos do best with a relatively dry setup and a separate humid hide rather than a wet enclosure, so persistent moisture on the skin or substrate can work against skin health.

Not every crusty patch is yellow fungus disease. Bacterial dermatitis, retained shed, trauma, burns, parasites, and nutritional or environmental problems can all mimic fungal dermatitis. That is why a visual guess is not enough, even when the lesion looks very suspicious.

Diagnosis starts with a hands-on exam and a close review of husbandry. Your vet will usually ask about humidity, temperatures, substrate, recent shedding problems, new reptile exposure, cleaning routine, and when the lesion first appeared. Photos showing how the patch changed over time can be very helpful.

Because several skin diseases look alike, your vet may recommend one or more tests rather than relying on appearance alone. Common options include skin cytology, fungal culture, biopsy with histopathology, and sometimes PCR testing to identify Nannizziopsis or related fungi. If the gecko is losing weight or seems systemically ill, your vet may also discuss blood work, imaging, or other tests to look for deeper disease or rule out additional problems.

Biopsy is often one of the most useful tests when the diagnosis is unclear or the lesion is severe. It can help distinguish fungal dermatitis from bacterial infection, trauma, neoplasia, or inflammatory skin disease. Culture or PCR may add organism-specific information, which can help guide treatment planning.

Try not to apply over-the-counter creams before the visit unless your vet has advised it. Topicals can change how the skin looks and may interfere with sample collection. If possible, keep the gecko warm, housed alone, and on clean paper substrate until your appointment.

Prevention starts with quarantine and cleanliness. Any new reptile should be housed separately from established pets, with separate feeding tools, hides, and cleaning supplies. Wash hands between animals, and disinfect enclosure items regularly. If one reptile develops suspicious skin disease, isolate that animal right away until your vet advises otherwise.

Good skin health also depends on good husbandry. Leopard geckos need a dry overall environment with an appropriate heat gradient and a humid hide for shedding, rather than a constantly damp enclosure. Dirty, wet substrate and chronically moist hides can irritate skin and may support infectious problems. Promptly remove waste, replace soiled substrate, and keep water dishes and decor clean.

Reduce skin injury whenever you can. Check for rough decor, unsafe heat sources, stuck shed around toes and tail, and any rubbing or trauma points in the enclosure. Small wounds and retained shed can become entry points for infection, especially in stressed geckos.

Finally, act early. If you notice a crusty patch that does not improve after the next shed, or a lesion that changes color, thickens, or spreads, book a reptile vet visit sooner rather than later. Early care is often less invasive, less costly, and easier on both the gecko and the pet parent.