What is a Fungal Infection?

Fungal infection can be defined as an infectious disease caused by fungi. A fungal infection is also referred to as mycosis. Fungal infections are contagious, spreading from person to person. Mycosis can be contracted even from an infected animal or contaminated soil. The most common symptom is skin rashes and vaginal discharge in females.

How do fungal infections occur?

Fungal species cannot penetrate the skin and generally enter the body through an injured part of the skin. The entry of the antigenic particle would trigger an immune response. But, if the immune system is too weakened to generate an appropriate immune response, or the fungus can evade the immune system, fungal infection occurs. This results in rapid proliferation, multiplication, and invasion of the fungi to the tissues and organs of the body.

Classification of fungal infections

Based on the site of infection, fungal infections can be classified into the following three types:

  • Subcutaneous fungal infection occurs when a fungus infects skin deeply, affecting the subcutaneous tissue.
  • Superficial fungal infections occur when the outer layer of skin, including nails and hairs, is affected.
  • Systemic fungal infections occur when the internal organs are affected. Fungi may enter through the skin, infect several organs such as the lungs, and even lead to severe health issues.

Introduction to Fungi

Fungi are eukaryotic organisms containing a cell wall composed of proteins, beta-glucans, and chitin. Fungi either possess unicellular (yeast) bodies or multicellular (molds) bodies. The bodies of multicellular fungi are composed of several filamentous structures called hyphae. These filamentous structures further form an interconnected network called mycelium. These structures are capable of penetrating surfaces with the help of enzymes released by the hyphae. The enzymes also degrade complex molecules and help fungi to absorb nutrients through mycelia. Fungal cells have membrane-bound nuclei and vacuoles. The chitin present in its cell wall makes them different from bacteria and plants. Fungi are heterotrophic as they depend on other organisms for nutrients and energy.

It exists in various environments and also plays an important role in our ecosystem. For example, it acts as a decomposer and helps in nutrient cycling.

Fungi can reproduce both sexually and asexually. Asexual reproduction in fungus includes fragmentation, budding, and production of spores. In contrast, sexual reproduction introduces the genetic variation in fungi. Sexual reproduction in fungi takes place in three stages:

  • Plasmogamy- It involves the fusion of the protoplasmic content of two fungal cells.
  • Karyogamy- It involves the fusion of the haploid nuclei of the two cells.
  • Meiosis- It refers to reduction division that restores the haploid state of the nuclei of the zygote formed.

The haploid nuclei get incorporated into meiospores.

A cylindrical thread-like structure shows different parts of the fungus, such as cell walls, vacuoles, nucleus, and septum. The hyphae are filamentous structures located at the outer side of the cell.
Structure of a fungal cell

Infection mechanism of fungi

  1. At first, it attack the keratin layer of the skin.
  2. It produces the keratinase enzyme, which degrades the keratin layer.
  3. It develops skin inflammation as the damaged keratinocytes release histamine, bradykinin, and prostaglandins.

The damaged cells release these chemicals stimulated by IgE antibodies released in response to foreign particles. These chemicals then cause swelling in tissues by stimulating the release and accumulation of fluid from blood vessels in the tissues.

An image shows a fungal cell infecting the keratin-rich layer of the human skin that is irregularly shaped embedded in the straight line-shaped membrane. The fungi release the keratinase enzyme, which degrades the keratin that leads to inflammation in the shape of a vertical dumbbell.
Mechanism of fungal infection

Types of fungal infections in human beings

There are several types of fungal infections. Some of the most common fungal infections of the skin are discussed below:

Athlete's foot

  • The other name of the athlete's foot is Tinea pedis. It is a type of fungal infection that occurs mainly in the feet but may also occur in the nails and hands.
  • The cause of this type of fungal infection is dermatophytes (fungi that grow in a warm and humid environment).

Jock itch

  • The other name of jock itch is Tinea cruris. It is a type of fungal infection that occurs mainly in the inner thigh and groin area.
  • It is also caused by dermatophytes.


  • The other name of ringworm is Tinea capitis. It is a type of fungal infection that mainly affects the skin and scalp.
  • It is caused by 40 different types of fungi. These types of fungi generally grow on the damp areas of the skin.
  • Ringworm is contagious as it can spread by direct contamination.

Toenail fungus

  • Tinea unguium is the other name for toenail fungus.
  • It mainly affects the toenails, fingernails, and nail beds.

Common symptoms of fungal infections

The symptoms of a fungal infection are as follows:

  • Redness on the skin
  • Blisters
  • Swelling
  • Burning
  • Peeling or scaly skin
  • Irritation
  • Ring-shaped patches

Risk of development of fungal infection

Several factors lead to a fungal infection. It includes environmental factors and the strength of the immune system of a person. The factors leading to fungal infection are described below:

  • Fungus generally grows in damp and moist areas. Therefore, staying for a long time in this condition increase the chance of getting infected by fungus.
  • A compromised immune system may lead to fungal infection. The infection level may get severe.
  • Nails or skin injuries can increase the risk of fungal infection as fungus can enter through the damaged part and invade the deeper tissues.
  • Certain types of medication can also increase the chance of fungal infection. For example, Candida albicans are present in human beings' gut in a small quantity, and the good bacteria in the gut prevent them from increasing in number. When antibiotics are administered due to bacterial infection, the beneficial bacteria are decreased or killed. This increases the fungal population and ultimately leads to fungal infection.

How does a fungal lesion look?

  • Rashes are bright red and spread in larger areas.
  • At the border of the lesion, the discoloration and scale are more intense.
The image shows a hand that has a round-shaped lesion known as ringworm. The magnified view of the ringworm is shown, which depicts that the ringworm is caused due to fungus and not due to any worms.
Magnified view of the ringworm

Consulting a doctor

One must consult a doctor if any of the following happens:

  • Fungal skin infection exaggerates in response after over-the-counter (OTC) fungal treatments.
  • Skin infection does not heal after OTC treatment.
  • Patches of hair loss are observed along with scaly skin.
  • A person has a weak immune system.
  • A diabetic patient has an athlete's foot.


Many antifungal medicines can cure fungal infections. These medicines act either by destroying the fungi or by inhibiting their growth. Mostly antifungal ointments, powders, gels, and sprays are used to treat skin infections.

The names of the medicines used for curing the infection are as follows:

  • Clotrimazole
  • Miconazole
  • Fluconazole
  • Ketoconazole

Note: The 'azole' written at the end of the medicines refers to a group containing an azole ring that inhibits the growth of the fungi. Azole is classified into two main groups based on the presence of nitrogens. For example, clotrimazole, miconazole, and ketoconazole contain two nitrogens in their azole ring. In contrast, fluconazole contains three nitrogens.

Side effects of antifungal drugs

  • Itching
  • Abdominal pain
  • Diarrhea
  • Rash
  • Abdominal pain
  • Feeling sick


To prevent the chance of infection, one must consider the following:

  • Skin must be kept clean by applying soap regularly.
  • Wash hands after touching any other person, objects, or animals as they may be contaminated with fungus.
  • Keep the skin dry in moisture-retaining conditions as moisture increases the chance of infection.
  • Practice good hygiene.
  • Clothes and shoes that breathe well must be used.
  • Dry off properly after a shower with a clean, dry towel.
  • Wipe off shared surfaces before touching, such as gyms.
  • Avoid touching infected animals.


  • A fungal infection may be easily cured by medication. Sometimes the infection may lead to a severe condition, taking several weeks and even months to cure.
  • An infected person must consult a doctor if there are severe symptoms.
  • Antifungal medicines can only treat fungal infections, and antibiotics do not work in curing the infection.

Common Mistakes

Students may get confused about the term ‘ringworm’ as it has 'worm' and classify it under a parasitic infection.

  • Ringworm is not a worm (parasite) but a fungal infection. The name is derived from the shape of the lesion caused by a fungus (worm in a ring shape).
  • All skin infections are not caused by fungus. Bacteria, viruses, and parasites can also cause skin infections and similar symptoms. Therefore, one must make sure of the cause of the infection before taking or applying any medication.

Context and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for the following:

  • Class 12-Biology
  • Bachelor of Science in Microbiology
  • Master of Science in Microbiology
  • Bachelor of Science in Immunology
  • Master of Science in Immunology
  • Bacterial Infection
  • Viral Infection
  • Parasitic Infection
  • Immunology

Practice Problems

Q1: Which of the following is the other name of the athlete's foot?

(a) Tinea cruris

(b) Tinea pedis

(c) Tinea versicolor

(d) Tinea unguium

Correct choice: (b)

Q2: When do superficial fungal infections generally occur?

(a) When the outer layer of skin, including nails and hairs, are affected.

(b) When a fungus infects skin deeply, affecting the subcutaneous tissue.

(c) When the internal organs are affected.

(d) None of the above

Correct choice: (a)

Q3: Which of the following is the causative agent of ringworm?

(a) Virus

(b) Fungi

(c) Bacteria

(d) All of the above

Correct choice: (b)

Q4: Which of the following disease shows scaly and dry lesions with a sensation of itch?

(a) Amoebiasis

(b) Elephantiasis

(c) Ascariasis

(d) Ringworm

Correct choice: (d)

Q5: Which of the following is/are the symptom(s) of ringworm?

(a) A red scaly rash

(b) Itching

(c) Ringed shaped rash

(d) All of the options are true

Correct choice: (d)

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