Nannizziomycosis in Leopard Geckos: Yellow Fungus and Other Fungal Skin Disease

Nannizziomycosis is a fungal infection caused by Nannizziopsis species. In reptile medicine, pet parents may still hear it called yellow fungus disease, although that older nickname is less precise because not every case looks bright yellow and not every fungal skin problem is caused by the same organism.

This infection targets keratinized tissue, so it often starts in the skin. A leopard gecko may develop discolored patches, crusts, thickened skin, ulcers, or areas that look like stubborn retained shed. In some reptiles, the disease can progress into deeper tissues and become much more serious over time.

Leopard geckos are not the species most commonly reported in the veterinary literature, but fungal skin disease can occur in reptiles broadly, and skin injury, stress, poor sanitation, and husbandry problems can make infection more likely. Because several skin conditions can look similar, your vet usually needs testing to confirm whether the problem is nannizziomycosis, another fungal infection, bacteria, trauma, or a shedding disorder.

The most important takeaway is speed. A small lesion that seems minor at first can worsen quickly, so early veterinary care gives your gecko the best chance for a manageable treatment plan.

Nannizziomycosis is caused by infection with Nannizziopsis fungi. These fungi are keratin-loving organisms, which means they can invade the outer skin layers and damaged tissue. In reptiles, fungal skin disease is more likely to take hold when the skin barrier is compromised or the immune system is under strain.

Common contributing factors include skin trauma, repeated retained shed, poor sanitation, chronic stress, improper temperatures, excessive humidity for the species, poor nutrition, and underlying illness. Merck notes that fungal skin infections in reptiles often gain entry through injured skin, and reptile references also list low immunity, husbandry problems, and unsanitary environments as important risk factors.

For leopard geckos, practical triggers may include abrasive cage injuries, toe or tail damage, dirty moist hides, chronically damp substrate, or enclosure conditions that interfere with normal shedding. A gecko that is already weakened by parasites, dehydration, or nutritional imbalance may also be less able to resist infection.

Pet parents should also know that the enclosure can matter. Emerging research in reptiles suggests environmental contamination may play a role, so your vet may recommend temporary hospital-style housing, easier-to-disinfect surfaces, and stricter cleaning during treatment.

Diagnosis starts with a hands-on reptile exam and a close look at the lesion pattern. Your vet will usually ask about humidity, temperatures, substrate, shedding history, diet, recent injuries, new reptiles in the home, and how fast the skin changes have progressed.

Because many skin problems look alike, diagnosis should not rely on appearance alone. Definitive diagnosis of nannizziomycosis is based on finding fungal elements in affected tissue and identifying the organism with histopathology plus culture, PCR, or similar lab testing. In practice, your vet may recommend skin scrapings or impression samples, fungal culture, biopsy, and PCR testing from crusts or tissue.

Additional tests may be needed if your gecko seems systemically ill. These can include bloodwork, imaging, and testing for other conditions that may be weakening the immune system or delaying healing. Culture results can take time, so your vet may discuss starting supportive care while waiting for confirmation.

This is one reason early visits matter. A small biopsy or targeted sample from an early lesion is often easier to manage than trying to sort out a widespread infection after tissue damage has become severe.

Prevention starts with strong basic husbandry. Keep your leopard gecko in a clean enclosure with appropriate heat gradients, species-appropriate humidity, a properly maintained humid hide, and surfaces that support normal shedding without causing skin injury. Good sanitation matters because fungal organisms can persist in the environment, especially where organic debris and moisture build up.

Check your gecko's skin during and after every shed. Look closely at the toes, tail tip, belly, and any area that seems discolored or rough. Repeated retained shed, small wounds, and chronic dampness can create an opening for infection, so early correction is important.

Quarantine new reptiles, avoid sharing tools between enclosures without disinfection, and clean hides, bowls, and decor regularly. If your gecko has had a fungal skin problem before, ask your vet what disinfecting approach and recheck schedule make sense for your home setup.

Nutrition and stress control also matter. A well-supported gecko with appropriate diet, supplementation, and low chronic stress is better positioned to maintain healthy skin and normal immune function. If you notice a lesion that does not improve with a normal shed cycle, book a visit with your vet sooner rather than later.