Fungal infections may call to mind itchy rashes, such as athlete’s foot. But the fungi normally found in soil and on plants, trees, skin, and more can cause a wide variety of infections. Some are surprisingly difficult to determine; others can be deadly serious. Here’s what to know about fungus and your health.

Fungus Can Affect Skin and Nails

Fungal infections of the skin and nails are common but sometimes misdiagnosed. About half of people with suspected nail fungus, which is marked by discolored, thick, and ragged toenails, don’t actually have it. And a ­recent study in the Journal of the American Academy of Dermatology found that only about half of dermatologists could identify a skin fungal infection by sight.

“It’s hard to tell a fungal infection from another skin condition, such as psoriasis, pityriasis rosea, or even something more serious like skin lymphoma,” says Adam Friedman, M.D., a dermatologist at the George Washington School of Medicine & Health Sciences in Washington, D.C.

Best steps: See your doctor if you’re unsure about what’s causing a rash or if a rash lasts more than 72 hours or is worsening. You might need a prescription antifungal, or you might have another problem.

Certain it’s a fungal infection? You can try an over-the-counter topical antifungal, such as clotrimazole (Lotrimin AF and generic) or terbinafine (Lamisil AT and generic).

For toenail problems, your doctor will probably send a sample of your toenail, surrounding skin, or debris under a nail to a lab. If nail fungus is confirmed, prescription oral and topical drugs are available. Oral drugs are more effective than paint-on prescription products but can cause digestive discomfort, headache, and rash. 

Other Worrisome Fungal Infections

Fungal infections such as aspergillosis, blastomycosis, and Valley ­fever can settle in the lungs if you unknowingly inhale spores in the air. The first two generally cause illness only in people with lung disease or a weak immune system. Valley fever, which is found in the southwestern U.S., can cause symptoms often mistaken for pneumonia, especially in older adults.

Best steps: If you have a cough, fever, headache, and chills and have been in a high-risk area, ask a doctor to test you for Valley fever.

“People don’t realize they’re at risk if they simply pass through the Phoenix airport, since they can inhale spores indoors,” says John Galgiani, M.D., an infectious-disease specialist at the University of Arizona College of Medicine. Severe cases may require a prescription antifungal such as fluconazole (Diflucan and generic) or itraconazole (Sporanox and generic). 

Some Fungal Infections Are Potentially Deadly

Candida (yeast) fungus commonly lives in the gastrointestinal tract and on skin without causing problems—though an overgrowth can cause yeast infections of the vagina or mouth and throat.

But if you are in intensive care or are hospitalized and have a central line (a thin tube inserted into a large vein), diabetes, or an immune system weakened by a transplant or chemotherapy, the fungi can cause serious bloodstream infections.

And a more recently identified yeast, Candida auris, can cause fatalities within 30 days in up to 40 percent of those infected. “Some strains of C. auris are resistant to all three major classes of antifungal drugs, which we’ve never seen before with Candida,” says Tom Chiller, M.D., chief of the Centers for Disease Control and Prevention’s Mycotic Diseases Branch. Although this yeast is rare in the U.S., new cases continue to be reported.

Best steps: If you (or a family member) are in one of the risk groups noted above, make sure that staff and visitors wear gloves and gowns and wash their hands when entering your room, and that the hospital cleans the room properly. The CDC recommends a hospital-grade disinfectant registered with the Environmental Protection Agency that’s effective against Clostridium difficile, such as Lysol Brand Disinfectant Bleach Plus or Virasept.

Question the use of IV antibiotics, which hike the risk of invasive candidiasis, says David Denning, M.D., a professor of infectious diseases in global health at the University Hospital of South Manchester in the U.K.

If you notice signs of invasive candidiasis (fever and chills that don’t improve despite antibiotics), call it to the attention of a health professional. Treatment is usually IV antifungals. For Candida auris, the CDC recommends three antifungals: anidulafungin (Eraxis), caspofungin (Cancidas and generic), and micafungin (Mycamine).