Fungal infections are diseases caused by tiny organisms called fungi that can affect your skin, nails, hair, or even internal organs like your lungs. While most fungal infections are not life-threatening and mainly affect the outer layers of the body, they can cause uncomfortable symptoms like itching, redness, and rashes that may persist without proper treatment.

What Are Fungal Infections?

Fungal infections, also known as mycosis, occur when harmful fungi invade the body and multiply beyond what your immune system can control. Fungi are living organisms that belong to their own kingdom, separate from plants, animals, and bacteria. While millions of fungal species exist in the world, only a few hundred are known to cause disease in humans^[1][2].

Fungi reproduce by releasing microscopic particles called spores into the air or environment. These spores can land on your skin or be inhaled into your lungs. Many fungi naturally live on and inside the human body, including in the mouth, digestive tract, and on the skin. Under normal circumstances, they remain harmless. However, when conditions allow them to overgrow, they can cause infections^[1].

Fungal infections typically appear on the skin, nails, hair, or mucous membranes such as the mouth, throat, or vagina. These are called superficial infections. However, fungi can also penetrate deeper into the body and affect internal organs like the lungs, brain, or heart, causing more serious systemic infections^[1][5].

Epidemiology: How Common Are Fungal Infections?

Fungal infections are remarkably common worldwide. More than one billion people get a fungal infection each year^[2]. Superficial infections of the skin and nails are cited as the most common form, affecting up to 20 to 25 percent of the world’s population at any given time^[11].

The burden of fungal disease extends beyond simple skin conditions. Serious fungal infections affect approximately 300 million individuals globally, and it is estimated that more than 1.5 million people die from these infections each year^[8]. In recent decades, fungi have emerged as significant threats in healthcare settings. Yeasts and molds now rank among the ten most frequently isolated pathogens in patients with compromised immune systems. For example, Candida, a common yeast, has become the fourth leading bloodstream isolate in hospitals in the United States^[3].

Fungal infections can affect anyone, regardless of age or gender. However, certain populations face higher risks. Superficial infections like athlete’s foot are common among otherwise healthy people, particularly athletes who frequent warm, moist environments like locker rooms. Vaginal yeast infections are very common among women, with most women experiencing at least one in their lifetime^[2].

Causes: What Triggers Fungal Infections?

Fungal infections develop when fungi that would normally remain harmless begin to multiply uncontrollably. This overgrowth happens when conditions become favorable for fungal reproduction. The primary causes depend on the type of fungus and where it grows on or in the body.

Many fungal infections start when spores that are naturally present in the environment come into contact with the body. Fungi thrive in soil, on plants, in water, and in the air. When spores land on the skin or are breathed into the lungs, they can establish an infection if the body’s defenses allow them to multiply^[1][6].

Some fungi, particularly those called dermatophytes, live off keratin, a protein found in skin, hair, and nails. These fungi cause infections like ringworm and athlete’s foot. They spread easily from person to person through direct contact or by touching contaminated surfaces like shower floors, towels, or shared sports equipment^[1][13].

Other fungal infections result from an imbalance in the body’s natural microbial environment. For instance, yeast such as Candida albicans normally lives on the skin and in areas like the mouth, throat, and vagina. When bacteria that usually keep these fungi in check are killed off—such as when someone takes antibiotics—the yeast can multiply out of control and cause symptoms. Similarly, changes in hormone levels, stress, or a diet high in sugar can encourage yeast overgrowth^[4][6].

Risk Factors: Who Is Most at Risk?

While anyone can develop a fungal infection, certain factors increase the likelihood of infection, especially severe forms. The most significant risk factor is having a weakened immune system. People with conditions that suppress immunity are at much higher risk for serious fungal infections^[1][2].

Individuals with HIV/AIDS, cancer, or those undergoing cancer treatments like chemotherapy face elevated risk. People taking medications that suppress the immune system—such as those used to prevent organ transplant rejection or to treat autoimmune diseases—are also vulnerable. Conditions like diabetes or poor circulation further increase susceptibility, particularly to nail and skin infections^[1][6].

Environmental and behavioral factors play a role as well. Warm, moist environments are ideal breeding grounds for fungi. Athletes who sweat heavily and spend time in communal showers or locker rooms are more prone to infections like athlete’s foot and jock itch. People who wear tight clothing, fail to change out of damp garments, or do not dry themselves thoroughly after bathing also face increased risk^[1][13].

Certain life stages and circumstances raise vulnerability. Pregnant women may experience hormonal changes that promote yeast infections. Babies wearing wet diapers for extended periods can develop diaper rash, a form of yeast infection. Elderly individuals are more susceptible to nail fungus due to factors like slower nail growth, reduced blood flow, and weakened immunity^[11][13].

People who have recently spent time in intensive care units or hospitals are at higher risk for severe healthcare-associated fungal infections. This is because they often have weakened immune systems due to underlying illness, medical procedures, or malnutrition. Long-term or high-dose antibiotic use can also disrupt the body’s natural balance of bacteria and fungi, leading to overgrowth of harmful fungi^[2][11].

Symptoms: How Fungal Infections Affect the Body

The symptoms of a fungal infection vary depending on the type of infection and the part of the body affected. Most superficial fungal infections cause visible changes to the skin, nails, or mucous membranes, along with discomfort.

Fungal infections of the skin often present as red, itchy, and scaly rashes. The affected area may appear swollen or bumpy, and in some cases, the rash forms a distinctive ring shape with clearer skin in the center, as seen in ringworm. The edges of the rash are typically more intense in color and scaling than the center. Some infections cause small, defined lesions or blisters at the borders of the affected area^[1][11].

Common skin symptoms include itching, stinging, or burning sensations. The skin may peel, crack, or develop patches that are lighter or darker than the surrounding skin. For example, tinea versicolor causes discolored patches, while athlete’s foot leads to white, peeling skin between the toes^[1][4].

Fungal infections of the nails, called onychomycosis, cause nails to become discolored, often turning yellow, brown, or white. The nails may thicken, become brittle, and crack or crumble easily. In severe cases, the nail may separate from the nail bed^[1][13].

When fungi infect mucous membranes, such as in the mouth or throat, they can cause a condition called oral thrush. This appears as white or yellow patches inside the mouth, on the tongue, or in the throat. It may be accompanied by soreness, difficulty swallowing, or cracks at the corners of the mouth. Vaginal yeast infections cause itching, burning (especially during urination or intercourse), redness, swelling, and an unusual discharge that may resemble cottage cheese^[1][4].

More serious fungal infections affecting internal organs can cause symptoms such as fever, cough, shortness of breath, chest pain, headaches, or confusion. These systemic infections are less common but can be life-threatening, especially in people with weakened immune systems^[1][2].

Prevention: How to Reduce Your Risk

Preventing fungal infections largely revolves around reducing exposure to fungi and maintaining conditions that discourage fungal growth. Good personal hygiene is the foundation of prevention.

Keeping the skin clean and dry is essential. After showering, swimming, or exercising, dry yourself thoroughly, paying special attention to areas where moisture can accumulate, such as between the toes, under the breasts, and in skin folds. Change out of wet bathing suits or damp clothing as soon as possible, and avoid sitting around in sweaty clothes^[1][13].

Wearing breathable fabrics like cotton helps keep the skin dry. Loose-fitting clothing allows air to circulate, which is particularly important in warm, humid weather. Tight garments trap moisture and heat, creating an environment where fungi can thrive. Change undergarments and socks at least once daily, or more frequently if they become damp^[13].

In communal or public areas like locker rooms, gym showers, and swimming pools, always wear protective footwear such as flip-flops or water shoes. These environments are common places where fungal spores spread. Avoid sharing personal items like towels, shoes, clothing, or grooming tools, as these can transfer fungi from one person to another^[1][13].

For those prone to yeast infections, maintaining a healthy balance of bacteria and yeast is important. Avoid unnecessary antibiotic use, as antibiotics can kill beneficial bacteria that keep yeast in check. Eating a balanced diet and managing conditions like diabetes can also help prevent overgrowth^[4].

If you have a weakened immune system or chronic health conditions, work closely with your healthcare provider to manage your health. This may include controlling blood sugar levels if you have diabetes, following medication regimens carefully, and seeking prompt treatment for any signs of infection^[1].

Pathophysiology: How Fungal Infections Develop

Understanding how fungal infections develop in the body helps explain why they occur and how they cause symptoms. Fungi are primarily opportunistic pathogens, meaning they typically only invade the body when natural defenses are compromised. Most of the time, humans coexist peacefully with fungi, but when the defense system is damaged or overwhelmed, infections emerge^[3].

Fungi are present everywhere in the environment. When fungal spores come into contact with the skin, they may land on the surface without causing harm. However, if the skin is broken through a cut, scrape, or abrasion, fungi can enter beneath the surface. Once inside, they begin to multiply if conditions are right. Warm, moist environments with limited airflow are ideal for fungal growth, which is why infections commonly occur in skin folds, between the toes, and in the groin area^[1][6].

Dermatophytes, the fungi responsible for infections like ringworm and athlete’s foot, specifically target tissues rich in keratin. They secrete enzymes that break down keratin, allowing them to feed on the protein and spread across the skin, nails, or scalp. As they multiply, the body’s immune system responds, causing inflammation, redness, and itching. The ring-shaped rash characteristic of ringworm forms as the infection spreads outward while the center begins to heal^[1][13].

In the case of yeast infections, the pathophysiology involves an imbalance in the body’s natural microbial community. Candida yeast normally resides on the skin and in mucous membranes without causing problems. Beneficial bacteria help keep Candida populations under control. When these bacteria are depleted—such as after antibiotic treatment—Candida can proliferate unchecked. The overgrowth leads to inflammation and the characteristic symptoms of itching, burning, and discharge^[4][6].

More serious systemic fungal infections occur when fungi are inhaled into the lungs or enter the bloodstream. In people with weakened immune systems, fungi that would normally be cleared by immune cells can establish infections in the lungs, brain, or other organs. These deep infections can spread rapidly and cause organ damage. The immune system’s weakened response allows the fungi to evade destruction, leading to potentially life-threatening illness^[2][3].

Modern aggressive medical treatments, such as chemotherapy, organ transplantation, and immunosuppressive therapies, have increased the incidence of invasive fungal infections. These treatments damage defense mechanisms to an extent that even fungi with low virulence can invade the body. The body’s inability to mount an effective immune response allows fungi to colonize tissues and cause severe disease^[3].