Fungal Infection

Fungal infections are classified into the following types based on the depth and location of the infection:

Superficial Fungal Infections

This type of fungal infection affects the outermost layers of skin, hair, and nails. It causes minor irritation, and is usually not serious. Here are some types of superficial fungal infections:

Dermatophytosis

Caused by dermatophytes (a group of fungi) such as Trichophyton, Microsporum, and Epidermophyton, this subtype is characterised by inflammation, itching, and the classic ring-shaped rash.

Candidiasis

Usually caused by Candida albicans, a type of fungus commonly found in small amounts in the human body, Candidiasis can cause inflammation, redness, and pain

Pityriasis Versicolor

Caused by yeast from the genus Malassezia (lipophilic/fat-loving, yeast-like fungi) that are naturally found on the skin of humans and many animals, this type of superficial fungal infection can lead to formation of discoloured patches

Subcutaneous Fungal Infections

Unlike superficial fungal infections that affect the outermost layers of the skin, subcutaneous fungal infections involve deeper layers of the skin. A subcutaneous fungal infection rarely spreads internally unless the patient is immunocompromised. Below are the main types of subcutaneous fungal infections:

Sporotrichosis

Also known as “rose gardener’s disease” (because it often affects people who handle soil, plants, or organic matter), sporotrichosis is caused by sporothrix schenckii, a dimorphic fungus (a type of fungus that can exist in two different forms). The infection initially causes a small, painless bump, which slowly enlarges and can turn into an ulcer. 

Chromoblastomycosis

A chronic subcutaneous fungal infection, chromoblastomycosis is caused by a group of dematiaceous fungi (characterised by the presence of melanin in their cell walls, which gives them a brown, black, or dark olive colour). A subcutaneous fungal infection causes lesions (appear as small papules or nodules) that can enlarge over time. 

Mycetoma

A chronic, progressively destructive infection of the skin, subcutaneous tissue, and sometimes bone, Mycetoma can be caused by more than 56 different species of fungi and bacteria. It is characterised by swelling, sinus tract formation, and discharge of grains (tiny coloured granules containing the causative organisms). In some cases, the infection can spread to deeper tissues. When this happens, the affected limb does not work properly or becomes severely deformed.

Systemic (Deep) Fungal Infections

Unlike many other types of fungal infections that affect the skin or mucous membrane, a systemic fungal infection damages internal organs such as the lungs or brain and can be life-threatening. Systemic fungal infections are more common among immunocompromised individuals. Following are some types of systemic fungal infections:

Histoplasmosis

Caused by Histoplasma capsulatum (a dimorphic fungus), histoplasmosis primarily affects the lungs but can spread to other parts of the body, especially in people with weakened immune systems.

Coccidioidomycosis

Also known as Valley Fever, Coccidioidomycosis is usually caused by Coccidioides immitis and Coccidioides posadasii ( two closely related species of dimorphic fungi). It can cause local inflammation and tissue damage.

Blastomycosis

Usually caused by Blastomyces dermatitidis and Blastomyces gilchristii, Blastomycosis can affect the lungs. In some people, especially those with weakened immunity, the fungus can spread (disseminate) via the bloodstream to the skin or bones.

The causes of fungal infections can be divided into two broad categories:

Exposure to Fungi

Fungi can enter the body (and cause infection) when a person comes in contact with fungal spores or active fungi in the environment. This can happen in the following ways:

• Many fungi including Aspergillus, Histoplasma, and Candida live in soil. When a person touches soil inhabited by fungi, they can enter their body and cause a fungal infection
• Aspergillus and some other fungi produce airborne spores that can enter the body through respiratory droplets 
• Fungi such as Sporothrix schenckii can infect gardeners or farmers through scratches
• Some fungi including dermatophytes (the fungi that cause ringworm) spread by skin-to-skin contact with an infected person/animal or through shared personal items (towels, shoes)

Internal or Host-Related Causes (Predisposing Factors)

Here are some other ways in which fungi can invade the body:

• Many people with HIV/AIDS, diabetes patients, individuals undergoing cancer treatment, and organ recipients are immunocompromised. A weak immune system is unable to prevent fungi from entering the body and causing a fungal infection
• Some antibiotics and steroids kill helpful bacteria that keep fungi in check, allowing them to multiply 
• Surgical wounds, indwelling catheters, and traumatic injuriesallow fungi direct access to tissues or bloodstream
• Sweating and tight clothingand poor hygiene promote fungal overgrowth

Though fungal infections can affect anyone, the following risk factors can increase the chances of them occurring:

Hospitalisation 

Hospital floors and surfaces are covered in opportunistic fungi such as Candida, Aspergillus, and Mucorales. These and other fungi can easily enter hospitalised, especially immunocompromised patients’ bodies through the respiratory or GI tract. The longer a patient is hospitalised, the higher their risk of a fungal infection. 

Skin and Mucosal Barrier Disruption

The skin and mucosal barrier is the body's first line of defense against fungal infections. It prevents fungi from entering the body and causing infections. Indwelling devices, traumatic injuries, and eczema can damage this barrier, allowing pathogens including fungi to enter the body. 

Malnutrition

T cells (especially CD4+ helper T cells) help the body fight invaders including fungi. Malnutrition reduces the number of these cells, and those that are already present do not work properly. This leads to reduced cytokine production (cytokines are chemical messengers that coordinate the immune response). Malnutrition can also impair macrophage function (macrophages are small cells in the blood or lymph that kill invaders), increasing infection risk. 

Age 

Newborns and older adults are at higher risk for fungal infections as:

• At birth, the immune system is not fully developed. An underdeveloped immune system reduces the body's ability to identify and kill fungi. 
• Age related changes can negatively impact the immune system’s ability to fight off germs.

Genetics

Some inherited genetic mutations can affect components of the immune system or compromise the integrity of the skin and mucosal barrier, increasing vulnerability to fungal infections.

The symptoms of fungal infections can vary depending on the type of fungus, the affected body part, and whether the person’s immune system is working properly. Here are some common fungal infection symptoms:

Itchy, Red, Scaly Patches

Once fungi enter the body, they irritate the skin and trigger an immune response, which causes the body to release histamines (chemicals naturally produced by the body). This leads to itching and inflammation. As a result, the body sends more blood to the affected area. Increased blood flow is a common cause of redness. Redness caused by a fungal infection can be accompanied by flaking that occurs when fungi feed on keratin, causing the outer layer of skin to break down.

Ring-shaped Rashes 

Some fungi grow outward in a circular fashion from the initial site of infection. As a fungus spreads outward it continues infecting fresh skin, while the centre of the infection may begin to heal due to the body’s immune response. This results in a clearer or less inflamed centre. The edges of the rash remain active, red, raised, and possibly scaly or itchy, giving the appearance of a ring.

Hair Loss in Circular Patches 

Dermatophytes such as Trichophyton and Microsporum cause Tinea capitis– a fungal infection of the scalp. As these fungi spread on the scalp, they damage hair shafts and follicles, leading to hair breakage. Hair falls out or breaks in well-defined, round or oval patches, resulting in typical “ring-like” appearance.

Thickened, Discoloured, and Brittle Nails

Here are some ways in which dermatophyte infections (caused by a group of fungi called dermatophytes) can lead to thickened, discoloured and brittle nails:

• Dermatophytes invade the nail bed and keratinised tissues (contain keratin-a protein), causing nails to produce more keratin in response to the damage. This leads to thickened nails
• Fungi can produce pigments and break down nail tissue, leading to discolouration 
• Some fungal infections weaken the nail structure by degrading keratin. This often results in brittle nails 

Fever

When fungi enter the body and begin to grow or spread, the immune system releases pyrogenic cytokines (a group of signaling proteins), which signal the brain’s hypothalamus to increase body temperature. Increased body temperature leads to fever.

Timely, accurate fungal infection diagnosis helps doctors identify the root cause of the infection and create effective treatment plans. Here are some diagnostic techniques doctors use to diagnose fungal infections:

Physical Examination

Many fungal infections are diagnosed on the basis of a physical examination, which involves visually inspecting the affected area for redness white patches, scaling, and thickened, discoloured nails. 

KOH Test

A simple and non-invasive test used to diagnose fungal infections, a KOH test involves taking a skin sample, treating it with potassium hydroxide (KOH) and viewing the sample under a microscope. KOH dissolves skin cells, making hyphae or spores visible. 

Fungal Culture Test

The gold standard test for diagnosing a fungal infection, a fungal culture test can help identify the specific fungus causing the infection. In this test, a skin, nail, hair, blood, sputum, urine or tissue sample is collected and placed on a special nutrient medium in the lab that promotes fungal growth. A lab technician observes the sample under a microscope to confirm the presence of a fungus. 

Serological Tests

Usually ordered when an invasive fungal infection is suspected or the patient is immunocompromised, galactomannan, β-D-glucan, cryptococcal antigen test and some other serological tests can help detect fungal antigens or antibodies in blood or body fluids. A serological test involves taking a blood sample and spinning it at high speeds in a lab to separate the serum—the clear fluid part of the blood that contains antibodies.

Biopsy 

In a biopsy, a tissue sample is taken and stained with PAS or GMS stains (special histological stains used by pathologists to detect fungal infections). A lab technician examines the sample under a microscope to identify fungal structures.

Effective fungal infection treatment helps prevent complications, improving quality of life. Here are some fungal infection treatment options:

Antifungals 

Topical antifungals are used to treat mild or superficial infections. Oral or intravenous antifungals, on the other hand, can help the body fight moderate to severe and invasive fungal infections. 

How do antifungals work? Ergosterol is a crucial component of the cell membrane of a fungus. Antifungals block enzymes involved in ergosterol production. Without ergosterol, the cell membrane becomes weak and leaky and dies.

Management of Underlying Conditions

Some health conditions such as diabetes and HIV/AIDS can increase one’s risk for a fungal infection. People living with these health conditions should take medications prescribed by their doctor and follow their instructions to manage their condition. 

Surgery

When non-surgical treatment options fail, a surgery may be performed to:

• Remove necrotic (dead) or infected tissue that does not respond to antifungal drugs
• Remove crusts or blood clots from nasal and sinus cavities 
• Amputate a severely infected limb 
• Drain abscesses

You can significantly reduce your risk of fungal infections by adopting simple, yet effective prevention strategies.

Prioritise Personal Hygiene

Poor hygiene often contributes to fungal infections. Maintain good personal hygiene by bathing daily with mild soap and water, thoroughly drying your skin, especially between toes and in body folds. Remember to change socks, underwear, and clothes daily, and avoid sharing personal items like towels, combs, shoes, socks, or nail clippers.

Keep Skin and Feet Dry

Fungi thrive in moist environments. To prevent their growth, apply an antifungal powder to your feet after bathing. Opt for shoes made from breathable materials and wear moisture-wicking socks. Going barefoot at home can also help keep your feet dry.

Use Medications Wisely

Only use antibiotics and steroids as instructed by your physician. Antibiotics can disrupt the balance of beneficial bacteria that keep fungi in check, while both topical and systemic steroids can suppress your immune system, potentially leading to fungal overgrowth.

Emphasize Nail and Scalp Care

Fungi often enter the body through breaks in the skin, dirt under nails, and hair follicles. Keep your nails trimmed and avoid artificial nails or salons that don't follow strict hygiene protocols. Wash your hair regularly and avoid sharing combs or hair accessories.

Pay Attention to Your Clothing

Tight, non-breathable clothes can trap sweat and heat, creating an ideal environment for fungal growth. Instead, opt for loose, light-coloured clothing and undergarments made from breathable fabrics that help keep your body cool and dry.

Though most fungal infections are harmless, some can lead to the following complications if left untreated:

Secondary Bacterial Infection

Fungal infections can damage the skin or mucous membranes, weakening the body's first line of defense. This allows bacteria to enter the body and cause a bacterial infection. 

Nail Deformity or Permanent Nail Damage

Some fungi can invade the keratin of the nail plate, nail bed, and surrounding tissues, weakening the nail structure. A persistent infection causes chronic inflammation around nails. This leads to irreversible damage to the nail matrix. 

Organ Failure

When an invasive or systemic fungal infection occurs, the fungus causing the infection can enter the bloodstream and spread to multiple organs inducing the brain, kidneys, liver, lungs, or heart. In such cases, fungi can invade and destroy tissue, causing necrosis, inflammation, and loss of organ function.

Vision Loss or Blindness

When fungi invade the interior of the eye, they can cause inflammation and destroy internal eye structures or lead to retinal detachment or scarring. If left untreated, such infections can cause permanent vision loss. 

Chronic Respiratory Issues 

Some fungi can infect lung tissues by triggering persistent inflammation and causing tissue damage, or leading to structural changes in the respiratory system that can result in chronic respiratory problems over time.

Are fungal infections contagious?

Yes, some fungal infections, like ringworm and athlete’s foot, can spread from person to person through direct contact or by sharing contaminated items such as towels or footwear.

How long does it take to recover from a fungal infection?

Recovery time varies depending on the type of infection and its severity. Mild superficial infections may clear within a few weeks with treatment, while deeper or systemic infections may require prolonged therapy and close medical monitoring.

Can fungal infections come back after treatment?

Yes, fungal infections can recur, especially if underlying risk factors like poor hygiene, damp environments, or compromised immunity are not addressed. Following your doctor’s advice and preventive measures can help reduce recurrence.

Are there any dietary changes that can help prevent fungal infections?

While no specific diet can prevent all fungal infections, reducing excessive sugar intake and maintaining a balanced diet can support a healthy immune system, which plays a role in fighting off infections.

Do fungal infections always cause symptoms?

Not always. Some people may carry certain fungi without showing symptoms, while others may develop visible or systemic signs, especially if their immune system is compromised.

Can I use over-the-counter antifungal creams without consulting a doctor?

For minor superficial infections, over-the-counter antifungal creams may help, but if symptoms persist, worsen, or involve the nails, scalp, or deeper tissues, it is crucial to consult a doctor for proper evaluation and treatment.

Is it safe to continue daily activities while being treated for a fungal infection?

In most cases, yes, but it depends on the severity and type of infection. Your doctor may advise certain precautions, such as keeping the affected area covered, avoiding communal showers, or limiting strenuous activities if you have systemic infections.

How are fungal infections different from bacterial or viral infections?

Fungal infections are caused by fungi, which are different organisms from bacteria and viruses. They often require different diagnostic approaches and treatments, such as antifungal medications, rather than antibiotics or antivirals.

Can pets spread fungal infections to humans?

Yes, pets can carry certain fungi like those causing ringworm, which can be transmitted to humans through direct contact. Maintaining pet hygiene and consulting a vet if your pet shows signs of a skin infection is advisable.

Does climate affect the likelihood of getting a fungal infection?

Yes, warm and humid climates create favourable conditions for fungi to thrive, increasing the risk of infections, particularly skin and nail fungal infections.

Reviewed by Dr. Sakshi Srivastava, Principal Consultant - Dermatology, on 09 July 2025.