Nail fungus, or onychomycosis, is a common condition where fungal organisms infect the nail. This infection can affect fingernails but is far more prevalent in toenails. Understanding how fungus grows on nails involves identifying the types of fungi responsible, how they gain entry, their growth mechanisms within the nail, and the visible changes that occur as the infection progresses.
The Fungal Culprits
Nail infections are primarily caused by dermatophytes, a group of fungi that thrive on keratin, the protein making up nails, hair, and skin. Trichophyton rubrum is the leading dermatophyte responsible for most nail fungal infections, particularly those affecting the toenails.
While dermatophytes account for the majority of cases, other fungal organisms can also cause onychomycosis. Yeasts, such as Candida species, frequently infect fingernails, especially when the nail has been previously damaged or is often exposed to water. Non-dermatophyte molds, including species like Aspergillus and Fusarium, are less common but can also be involved, often requiring pre-existing nail trauma for infection.
Initial Entry and Establishment
Fungal organisms typically gain access to the nail unit through microscopic openings. These entry points can include tiny cuts or small separations between the nail and the nail bed or surrounding skin. Minor trauma to the nail can create these vulnerabilities, allowing the fungus to establish.
Exposure to fungi is common in warm, moist environments where these organisms thrive. Public showers, swimming pools, locker rooms, and gyms are frequent sources of fungal spores. Direct contact with an infected person or contaminated items like unwashed towels, shoes, or nail-grooming tools can also facilitate transmission. A pre-existing fungal skin infection like athlete’s foot can also spread to the nails.
The Growth Mechanism
Once inside, fungi utilize the nail’s primary structural component: keratin, the hard protein that gives nails their strength and form. They produce specialized enzymes, known as keratinases, which break down the tough keratin, allowing the fungi to digest the nail material.
As the fungi feed on the broken-down keratin, they multiply and spread throughout the nail plate. The infection often starts from the nail’s free edge or sides, slowly progressing underneath the nail towards the cuticle and nail matrix. This internal proliferation results in the accumulation of fungal debris and altered nail material, contributing to the visible changes. The continuous digestion of keratin by the growing fungal colony gradually compromises the nail’s structural integrity.
Visible Progression and Contributing Factors
As the fungal infection advances, the nail undergoes noticeable transformations. Early signs often include a white or yellow-brown spot appearing under the nail tip. Over time, the nail becomes discolored, turning yellow, white, brown, or even green. The nail may also thicken, become brittle, crumbly, or ragged, and sometimes distort in shape. In some cases, the nail may partially or completely separate from the nail bed, a condition known as onycholysis.
Several factors can contribute to the growth and persistence of nail fungus. Warm, moist environments, often created by tight-fitting footwear that lacks proper ventilation, provide an ideal breeding ground for fungi. Individual health factors also play a role, including a weakened immune system, aging (as nails grow slower and become more brittle), and underlying health conditions such as diabetes or poor circulation. These systemic issues can reduce the body’s ability to fight off the infection and can lead to more severe or chronic cases.