Candida is a type of yeast, a single-celled fungus that naturally lives on and inside the human body. It’s found in small amounts on your skin, in your mouth, in your intestines, and in the vaginal tract. Most of the time it causes no problems at all. But when conditions shift in its favor, Candida can multiply beyond its normal levels and cause infections ranging from mild and annoying to life-threatening.
Where Candida Lives in a Healthy Body
Candida is part of your normal microbiome. Your body hosts small colonies of it alongside trillions of bacteria, and under healthy conditions, those bacteria keep Candida populations in check. Your immune system also plays a constant role in surveillance, preventing the yeast from growing beyond its usual numbers.
This balance is the key concept for understanding every Candida-related problem. The yeast itself isn’t inherently dangerous. It becomes a problem only when something disrupts the ecosystem it lives in or weakens the immune defenses that keep it contained.
How Harmless Yeast Becomes an Infection
Candida has a trick that most yeasts don’t: it can change shape. In its normal, peaceful state, it exists as round yeast cells. But in response to cues from its environment (changes in pH, temperature, or nutrient availability), it can switch into an elongated, thread-like form called hyphae. These thread-like cells are more aggressive. They can physically penetrate tissue, anchor themselves more firmly, and trigger stronger inflammatory responses.
The most common trigger for overgrowth is antibiotic use. Antibiotics kill bacteria, including the beneficial ones that compete with Candida for space and nutrients in the gut, mouth, and vaginal tract. With that competition removed, Candida expands rapidly. This is why yeast infections so often follow a course of antibiotics.
Steroids, chemotherapy, and conditions that suppress the immune system have a similar effect. They don’t remove bacterial competition, but they weaken the immune surveillance that normally keeps Candida from gaining a foothold. Diabetes is another major risk factor, likely because elevated blood sugar provides extra fuel for yeast growth.
Types of Candida Infections
Candida infections fall into two broad categories: superficial (on the skin or mucous membranes) and invasive (in the bloodstream or internal organs). The superficial types are extremely common and rarely dangerous. Invasive candidiasis is rare but serious.
Vaginal Yeast Infections
Roughly 3 out of 4 women will experience at least one vaginal yeast infection in their lifetime. Symptoms include vaginal itching or soreness, pain during sex or urination, abnormal discharge (often thick and white), and redness or swelling of the vaginal walls. Pregnancy, hormonal birth control, diabetes, and recent antibiotic use all increase the risk.
Oral Thrush
Thrush appears as white patches on the inner cheeks, tongue, roof of the mouth, or throat. It often comes with a cottony feeling in the mouth, redness, loss of taste, and pain while eating or swallowing. Cracking at the corners of the mouth is another telltale sign. People with diabetes, HIV/AIDS, cancer, dry mouth, or dentures are more susceptible. Inhaled corticosteroids used for asthma are a well-known trigger, which is why rinsing your mouth after using an inhaler is standard advice.
Esophageal Candidiasis
When Candida infects the esophagus, it causes pain and difficulty swallowing. This form is much less common than thrush or vaginal infections and typically occurs in people with significantly weakened immune systems. It’s one of the most frequent infections in people living with HIV/AIDS.
Invasive Candidiasis
The most dangerous form occurs when Candida enters the bloodstream, a condition called candidemia. An estimated 25,000 cases occur in the United States each year, and Candida is a leading cause of hospital-acquired bloodstream infections. About one third of people with candidemia die during their hospitalization. Research comparing infected patients to similar uninfected patients found that the Candida infection itself was directly responsible for 19% to 24% of those deaths.
Invasive candidiasis typically affects people who are already critically ill. Risk factors include long stays in an intensive care unit, central venous catheters (IV lines placed in large veins), recent abdominal surgery, organ transplants, kidney failure, and premature birth. People who inject drugs also face elevated risk for bloodstream, heart valve, and bone infections from Candida.
The Species That Cause Problems
There are hundreds of Candida species, but only a handful cause most human infections. CDC surveillance data from 2017 to 2021 shows the breakdown for bloodstream infections: Candida albicans accounts for about 37% of cases, followed by Candida glabrata at 30%, Candida parapsilosis at 14%, and Candida tropicalis at 6%. The remaining cases involve less common species.
This matters because different species respond differently to antifungal medications. Candida glabrata, for instance, is naturally less susceptible to some of the most commonly used antifungals, which is one reason doctors identify the exact species when treating serious infections.
One species getting particular attention is Candida auris. First identified in 2009, it spreads easily between patients in healthcare facilities, can survive on surfaces for weeks, and is often resistant to multiple classes of antifungal drugs. The CDC classifies it as an urgent threat. It primarily affects people who are already very sick, particularly those in long-term care facilities.
How Candida Infections Are Diagnosed
For vaginal yeast infections, diagnosis is usually straightforward. A healthcare provider takes a small sample of vaginal discharge and examines it under a microscope, or sends it to a lab for a fungal culture. Oral thrush can often be identified by its distinctive white patches on visual exam alone.
Invasive candidiasis is harder to catch. The standard approach is drawing a blood sample and sending it to a lab to see if Candida grows in culture. This process can take several days, and blood cultures don’t always detect the infection, which is one reason candidemia can be difficult to diagnose quickly.
How Candida Infections Are Treated
Superficial infections like vaginal yeast infections and mild thrush are typically treated with antifungal medications that target the yeast’s cell membrane. These come in topical forms (creams, lozenges, suppositories) or oral tablets, and most people see improvement within a few days to a week. Over-the-counter options are available for uncomplicated vaginal yeast infections.
Invasive candidiasis requires stronger antifungal medications given intravenously in a hospital setting. There are several classes of drugs available, and the choice depends on which Candida species is involved, whether it shows drug resistance, and how sick the patient is. Treatment typically continues for at least two weeks after the yeast clears from the bloodstream.
Drug resistance is a growing concern across all types of Candida infections. Repeated or prolonged antifungal use can push Candida populations to develop resistance, making subsequent infections harder to treat. This is especially problematic with species like Candida auris, which can arrive already resistant to multiple drug classes.
Who Is Most at Risk
For superficial infections, the biggest everyday risk factors are antibiotic use, diabetes, pregnancy, hormonal contraceptives, smoking, and anything that suppresses the immune system. Inhaled steroids and conditions causing dry mouth also increase the likelihood of oral thrush.
For invasive disease, the risk profile shifts dramatically toward hospitalized and immunocompromised patients. Long ICU stays, IV lines, feeding through a vein (total parenteral nutrition), broad-spectrum antibiotics, chemotherapy, organ transplants, kidney failure requiring dialysis, and premature birth all raise the risk significantly. These aren’t factors most healthy people encounter in daily life, which is why invasive candidiasis remains primarily a hospital-associated infection.