Pain under the nail usually comes from one of a handful of common causes: a bruise from trauma, an infection at the nail fold, an ingrown nail, or pressure from a thickened or damaged nail. Less often, it signals something that needs closer medical attention, like a small tumor or a chronic skin condition affecting the nail bed. The location, timing, and type of pain all help narrow down what’s going on.
Trauma and Bruising Under the Nail
The most common reason for sudden pain under a nail is a subungual hematoma, which is blood trapped between the nail plate and the nail bed. This happens when you slam your finger in a door, drop something on your toe, or stub it hard against furniture. The nail bed has a rich blood supply, so even a modest crush injury can cause rapid bleeding underneath. The result is intense, throbbing pain and a dark red or purple-black discoloration that appears within hours.
The pain comes from pressure. Blood pools in a tight space with nowhere to go, and that buildup pushes against the nail bed’s dense network of nerve endings. Small hematomas that cover less than half the nail often resolve on their own as the blood slowly grows out with the nail over weeks. Larger ones, especially those covering more than 50% of the nail, may need to be drained by a doctor through a small hole in the nail plate. This procedure relieves the pressure almost immediately.
If you don’t remember any specific injury but notice a dark streak or spot under the nail that doesn’t grow out over several weeks, that’s worth getting checked. A bruise should migrate forward as the nail grows. A dark line or patch that stays in place, especially one where the pigment extends onto the skin around the cuticle, can in rare cases indicate melanoma under the nail. The key distinction: bruises move and fade, while melanoma stays put or expands.
Bacterial Infections at the Nail Fold
Acute paronychia is an infection of the skin right next to the nail, and it’s the second most common culprit behind sudden nail pain. It typically starts after a minor break in the cuticle from nail biting, aggressive manicuring, or picking at a hangnail. Bacteria, usually staph, slip through that small wound and multiply fast. Within a day or two, the nail fold becomes red, swollen, warm, and tender. If pus collects, you may see a whitish pocket along the side or base of the nail.
Most people show up for treatment within the first few days because the pain is hard to ignore. Mild cases sometimes resolve with warm soaks, but once pus has formed, it usually needs to be drained. In children who bite or suck their nails, the bacterial mix can include organisms from the mouth, which sometimes makes these infections more stubborn.
Chronic paronychia is a different story. It develops over weeks or months, often in people whose hands are frequently wet, like bartenders, dishwashers, or healthcare workers. The nail fold stays puffy and red but rarely forms a visible abscess. Instead, you lose the cuticle, the nail plate gradually thickens and discolors, and there’s a low-grade ache rather than sharp pain. Candida (a type of yeast) is frequently involved, sometimes alongside bacteria.
Fungal Nail Infections
Fungal infections of the nail itself, called onychomycosis, affect roughly 10% of the U.S. population and are far more common on toenails. They usually start at the tip or side of the nail and work their way back. Early on, you notice white or yellowish discoloration and the nail pulling away from the bed. Over time, the nail thickens, becomes brittle, and builds up chalky debris underneath.
The pain from a fungal nail isn’t always immediate. It develops gradually as the nail thickens enough to press into the nail bed, especially inside shoes. The subungual buildup of keratin debris creates constant low-level pressure. In advanced cases, the entire nail becomes thick and distorted, making it painful to wear closed-toe shoes or put any pressure on the toe. One specific subtype caused by molds (rather than the more common dermatophytes) tends to produce more noticeable pain and inflammation around the nail fold, sometimes with discharge.
Ingrown Nails
Ingrown nails are one of the most frequent causes of toenail pain, particularly on the big toe. The edge of the nail curves down and digs into the soft skin of the nail fold, causing tenderness, swelling, and redness along the side. If the skin breaks, bacteria can enter and turn it into a full infection with pus and granulation tissue (raw, bumpy tissue that bleeds easily).
Tight shoes, cutting nails too short or in a curved shape, and naturally curved nail plates all raise the risk. There’s also a less well-known condition called retronychia, where the nail grows backward into the proximal nail fold (the skin at the base of the nail) instead of forward. This typically follows trauma that disrupts normal nail growth. The old nail plate gets pushed back into the fold, causing chronic swelling, pain, and sometimes yellowish discoloration. It can look like a stubborn infection that won’t clear up, and it’s often missed on the first visit.
Glomus Tumors
If you have persistent, unexplained pain under a fingernail, especially pain that flares in cold temperatures and with even light touch, a glomus tumor is worth considering. These are small, benign growths of the tiny blood vessel structures that regulate temperature in your fingertips. They’re rare but frequently misdiagnosed because they’re so small they’re easy to miss on examination.
The classic pattern has three features: pinpoint tenderness in one specific spot under the nail, sharp pain triggered by cold exposure (like reaching into a freezer or holding a cold drink), and intense pain from minor bumps or pressure that wouldn’t normally hurt. You might see a faint blue-red spot under the nail, but not always. People often live with this pain for years before getting a diagnosis. Surgical removal resolves it.
Psoriasis and Other Inflammatory Conditions
Nail psoriasis is common in people who already have psoriasis on their skin or psoriatic arthritis. Up to 80% to 90% of people with psoriatic arthritis develop nail changes, largely because the disease targets the joint closest to the nail. When psoriasis affects the nail bed, it can cause the nail to lift off the bed, create salmon-colored “oil drop” spots visible through the nail plate, and produce a buildup of white, scaly debris underneath.
That debris buildup (subungual hyperkeratosis) creates the same kind of pressure-related discomfort as a thickened fungal nail. The nail may also develop tiny pits on its surface, ridges, or crumbling at the edges. If you have psoriasis elsewhere on your body and develop painful, thickened nails, the two are very likely connected.
Gout is another inflammatory condition that can cause nail pain, particularly in the toes. Urate crystals can deposit near the nail bed, creating hard, chalky lumps called tophi that press on surrounding tissue.
Other Causes Worth Knowing
A few less common causes round out the list:
- Foreign bodies: Splinters or small fragments of debris can lodge under the nail and cause localized pain that worsens with pressure.
- Bone growths: A bony spur (exostosis) on the tip of the finger or toe bone can push upward into the nail bed, creating persistent pain. Enchondromas, which are benign cartilage tumors inside the bone, can do the same.
- Medications: Certain chemotherapy drugs (particularly taxanes) and retinoids can cause significant nail pain, sometimes with nail loosening or inflammation of the nail folds.
- Herpetic whitlow: A herpes simplex infection of the fingertip that produces painful, clustered blisters on a red base, usually affecting the thumb. The pain and swelling can be severe.
Signs That Need Prompt Attention
Most nail pain resolves on its own or with straightforward treatment. A few patterns, however, warrant a faster trip to your doctor. Red streaks spreading away from the nail, increasing swelling that extends beyond the finger or toe, fever, or worsening pain after several days of home care all suggest the infection may be spreading to deeper tissue. In rare cases, untreated infections near the nail can reach the bone, causing a deeper infection (osteomyelitis) that requires more aggressive treatment.
A dark streak or spot under the nail that doesn’t grow out within two to three months, especially if the pigment bleeds into the surrounding skin at the cuticle, should be evaluated to rule out subungual melanoma. Pain under a nail that has lasted months with no clear cause, particularly with cold sensitivity, deserves investigation for a glomus tumor or bone-related issue, often with imaging.