Skin fungal infections are skin diseases caused by fungus, such as mold or mildew. The most common types of fungus that affect the nails include:
- Onychomycosis
- Fungal infection of the nails
- Tinea pedis (“athlete's foot”)
- A contagious fungal infection caused by a ringworm
Treatment to get rid of fungus on the nails includes:
- Over-the-counter (OTC) topical antifungal products for mild cases affecting less than 50% of one or two nails for onychomycosis
- OTC topical antifungal products to kill athlete’s foot fungus
- Chronic tinea pedis may require adjunctive therapy such as foot powder or talcum powder to prevent skin softening
- Chronic or extensive fungus on the nails may require prescription oral antifungals
- Terbinafine (Lamisil Oral Granules)
- Itraconazole (Sporanox)
- Fluconazole (Diflucan)
- Non-drug treatments
- Lasers emitting infrared radiation
- Photodynamic therapy using 5-aminolevulinic acid or methyl aminolevulinate followed by exposure to red light
- Iontophoresis and ultrasound are being studied for use to enhance the delivery of antifungal drugs to the nail plate
What Are Symptoms of Fungus on the Nails?
Fungal infections of the fingernails and toenails may also affect the skin.
Symptoms of fungal infections of the nails may include:
- Ring-shaped rash
- Skin redness
- Scaly, cracked skin
- Skin swelling
- Itching
- Blisters
- Deep fungal infections
- Red, swollen, peeling, itchy skin between the toes
- Soles, heels, and toenails may also be affected
- Skin on the feet may blister in severe cases
What Causes Fungus on the Nails?
Onychomycosis may be caused by:
- Dermatophytes such as Trichophyton rubrum (T. rubrum), T. interdigitale (tinea unguium)
- Yeasts such as Candida albicans and rarely, non-albicans Candida species
- Molds such as Scopulariopsis brevicaulis and Fusarium species.
Athlete’s foot (tinea pedis) is most often caused by human dermatophytes, a type of fungus transmitted by direct contact with human ringworm sores. Ringworm may also be acquired from the soil or through exposure to animals (commonly household pets).
Risk factors for developing athlete’s foot include:
- People who have a weakened immune system (such as from HIV/AIDS, cancer, chemotherapy, diabetes, or certain medications)
- Use of public showers or locker rooms
- Athletes involved in contact sports, such as wrestling
- Excessive sweating in tight shoes
- Close contact with affected animals such as household pets
- Working with soil that has ringworm fungus
- Living in a warm, humid climate
- Close contact with a person who is infected
- Sharing bedding, towels, or clothing with a person who is infected
How Is Fungus on the Nails Diagnosed?
Fungal infections of the nails are often diagnosed with a physical examination of the affected skin.
Tests that may be indicated to diagnose fungus on the nails include:
- Skin scraping to be examined under a microscope or sent to a laboratory for a fungal culture
- Ultraviolet light – can only diagnose two species: Microsporum canis and audouinii
From 
Skin Problems and Treatments Resources
Image source: iStock Images
https://www.cdc.gov/fungal/diseases/ringworm/index.html
https://www.uptodate.com/contents/dermatophyte-tinea-infections?search=fungal%20skin%20infection&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1
https://dermnetnz.org/topics/fungal-skin-infections/