Debris Under the Nail: What It Means

What the debris is

Under a normal nail, the nail bed is smooth and the nail plate is firmly attached. When the bed is inflamed or infected, its skin cells multiply and pile up as a dry, crumbly layer. This lifts the nail plate and creates a space where dirt, skin flakes, fungus and bacteria collect. Doctors look at the color, texture and pattern of the debris to work out the cause.

Common causes

Fungal nail infection

Onychomycosis is the most common reason for buildup under toenails. It usually starts at the tip or sides of the nail and spreads back. Typical signs:

• white, yellow or brown crumbly debris under the nail
• a thickened, brittle nail that lifts from the bed
• often affects one or a few toenails first, especially the big toe
• athlete's foot between the toes or on the sole

It is more common with age, diabetes, poor circulation, sweaty feet, communal showers and previous nail injury.

Nail psoriasis

Up to half of people with psoriasis have nail changes. Psoriatic nails show:

• silvery-white or yellowish buildup under the nail
• small pits on the nail surface
• yellow-brown "oil drop" or "salmon patch" spots
• lifting of the nail edge

It often affects fingernails and several nails at once. Nail psoriasis is linked with psoriatic arthritis.

Trauma and onycholysis

Repeated pressure from tight shoes, running, tapping long nails, or picking under the nails can separate the nail from its bed (nail separation). The space traps debris. A single big injury can leave old blood under the nail, which looks dark red, purple or black and grows out with the nail.

Bacterial infection

Pseudomonas bacteria growing under a lifted nail cause green or blue-black discoloration, often in people whose hands are often wet. Acute paronychia causes painful swelling and pus at the nail fold.

Less common causes

• Warts under or around the nail: rough growths that lift the nail
• Eczema and lichen planus affecting the nail bed
• Foreign bodies such as splinters
• Subungual melanoma: a rare skin cancer that starts as a brown or black band in the nail, which widens and may spread onto the surrounding skin (Hutchinson's sign). See melanoma.

Clues by appearance

How the cause is diagnosed

A doctor, dermatologist or podiatrist examines all nails, skin and feet. Because fungal infection and psoriasis look alike, a nail clipping or scraping is usually sent for microscopy, culture or PCR before starting long antifungal treatment. A dark streak may be examined with dermoscopy and sometimes biopsied.

Treatment

Fungal nails

• Oral antifungals such as terbinafine are the most effective, taken for about 6 weeks for fingernails and 12 weeks for toenails. Blood tests may be advised.
• Medicated nail lacquers or solutions for mild infection limited to part of the nail; they need daily use for many months.
• Treat athlete's foot at the same time.
• A clear nail takes 6 months (fingers) to 12 to 18 months (toes) to grow out, and recurrence is common.

Nail psoriasis

Treatment options include strong steroid or vitamin D creams applied to the nail folds, steroid injections into the nail fold, and systemic or biologic medicines when many nails or joints are involved.

Trauma and onycholysis

• Keep nails short and trimmed back to where the nail is attached.
• Wear roomy shoes and keep hands dry; use gloves for wet work.
• Do not dig under the nail to clean it, which worsens separation.

Infection

Pseudomonas often clears with keeping the area dry and trimming the lifted nail, sometimes with antibacterial solutions. Paronychia with pus may need draining and antibiotics.

Prevention

• Keep feet clean and dry and change socks daily.
• Wear sandals in communal showers and pools.
• Do not share nail clippers or files.
• Cut toenails straight across.
• Choose shoes with enough room in the toe box.

Frequently asked questions

What is the white stuff under my toenail?

White, crumbly buildup under a toenail is most often fungal infection. It can also be nail psoriasis or skin cells built up after repeated pressure from shoes. A clipping can be tested to confirm the cause before treatment.

Is debris under the nail a sign of fungus?

Often, but not always. Fungal infection is the most common cause, but psoriasis, trauma and nail separation produce similar buildup. Because antifungal treatment takes months, doctors usually confirm fungus with a lab test first.

Should I clean out the debris under my nail?

Gently trimming a lifted nail and washing the area is fine. Avoid digging deep under the nail with sharp tools, because this separates the nail further and lets infection in. A podiatrist can safely thin thick nails and remove debris.

Can nail psoriasis look like fungus?

Yes. Both cause thickening, lifting, discoloration and buildup under the nail. Clues to psoriasis are pitting, oil-drop spots, several fingernails affected and psoriasis elsewhere on the skin. Some people have both conditions at once.

When is debris under the nail serious?

It is serious when there is spreading redness, swelling, pus or fever, which suggest infection, or a dark streak that is widening or spreading onto the skin, which needs checking for melanoma. People with diabetes should have any nail change assessed.