A bump on your nail is usually caused by a minor injury to the nail’s growth center, a condition called Beau’s lines, or simply normal aging. Most nail bumps are harmless and grow out on their own within a few months. But the type of bump matters: horizontal ridges, vertical ridges, small dents, and raised lumps all point to different causes, and a few warrant a closer look from a dermatologist.
Horizontal Ridges and Grooves
Horizontal bumps or grooves that run side to side across your nail are called Beau’s lines. They happen when something temporarily disrupts nail growth at the base (the matrix), leaving a visible dent or ridge as the nail continues growing out. Common triggers include high fever, severe illness, surgery, injury to the finger, eczema around the nail, nutritional deficiencies, and chemotherapy. Essentially, your body diverted resources away from nail production during a stressful event, and the groove is a physical record of that pause.
If you can trace the timing back to a specific illness or injury, that’s likely your answer. Fingernails grow at roughly 3.5 mm per month, so you can estimate when the disruption happened by measuring how far the ridge is from the cuticle. A groove sitting halfway up a nail that’s about 14 mm long appeared roughly two months ago. The bump will grow out completely as the nail replaces itself, which takes about four to six months for fingernails and closer to a year for toenails.
A single groove on one nail usually points to local trauma, like slamming it in a door or catching it on something. Matching grooves across multiple nails at the same position suggest a systemic event, something that affected your whole body at once.
Vertical Ridges
If the bump runs lengthwise from the cuticle toward the tip, it’s most likely a vertical ridge. These are extremely common and almost always harmless. They become more noticeable with age as the nail matrix gradually produces keratin less evenly. Think of them as the nail equivalent of wrinkles.
Vertical ridges don’t signal a nutritional deficiency or serious disease in most cases. If they bother you cosmetically, gently buffing the nail surface can smooth them out, though overdoing it thins the nail. No treatment is needed.
Small Dents or Pitting
Tiny, pinpoint depressions in the nail surface, sometimes described as bumps in reverse, are called pitting. They look like someone pressed the tip of a pin or pencil into the nail. Individual pits can be as small as 0.4 mm or as large as 2 mm, and you might have just one or two per nail or more than ten.
Nail pitting is one of the hallmark signs of psoriasis. It affects over 50% of people with psoriasis and around 86% of those with psoriatic arthritis. If you’re noticing pitting along with patches of dry, scaly skin elsewhere on your body, or if your joints feel stiff and swollen, psoriasis is a strong possibility. Pitting can also show up with alopecia areata and eczema, though psoriasis is the most common link.
Washboard Nails From Picking
If your thumbnail (or both thumbnails) has a series of parallel horizontal ridges running down the center, giving it a rippled or washboard-like texture, the cause is likely a habit you may not even realize you have. Repeatedly pushing at, picking, or rubbing the cuticle with an adjacent finger damages the nail matrix underneath, producing a row of evenly spaced bumps as the nail grows out.
This is called habit-tic deformity, and it’s surprisingly common. In more pronounced cases, the cuticle disappears entirely and the half-moon at the base of the nail looks enlarged and swollen. The fix is straightforward: stop the repetitive trauma. Covering the cuticle with a bandage or applying a bitter-tasting nail product can help break the cycle. Once the habit stops, the nail regrows normally within a few months.
Fungal Infections
A bump that comes with thickening, yellowing, or crumbling of the nail could be a fungal infection. The fungus grows under the nail plate and produces a buildup of debris that pushes the nail upward, creating a raised, uneven surface. The nail may turn yellow-white or brown-black and eventually separate from the nail bed. In some cases, a dense mass of fungal material forms beneath the nail, creating a distinct localized bump.
Fungal nail infections are slow to develop and slow to treat. They won’t resolve on their own, and over-the-counter topical treatments have limited success because the fungus sits beneath the hard nail plate. Prescription oral antifungal medications are more effective but require several months of treatment because you’re essentially waiting for a completely new, healthy nail to grow in.
Glomus Tumors and Other Growths
Rarely, a bump on the nail is caused by a small growth beneath the nail plate. The most well-known is a glomus tumor, a benign growth in the tiny blood vessels under the nail. It’s not cancerous, but it’s intensely painful. The classic signs are sharp, localized pain that you can pinpoint with the tip of a pen, extreme sensitivity to cold (dipping the finger in cold water triggers severe pain), and episodes of throbbing that come and go. If pressing a pencil tip against different spots on the nail reproduces the pain in one exact location, that’s a strong indicator. These are removed surgically, and the pain resolves almost immediately afterward.
Dark Streaks and Color Changes
If your nail bump is accompanied by a dark brown or black streak running lengthwise, this needs prompt evaluation. A new or changing dark streak can be a sign of subungual melanoma, a rare but serious form of skin cancer that develops under the nail. Dermatologists use a set of criteria to assess risk: age between 50 and 70, a band that is black or brown and wider than 3 mm with blurry borders, changes in size or color over time, location on the thumb or index finger of the dominant hand, and pigment that extends onto the surrounding skin fold (a finding called the Hutchinson sign). People with darker skin tones, including those of African, Asian, or Native American descent, have a higher incidence.
Not every dark line is melanoma. Many are benign pigmented bands, especially in people with darker skin, where they’re common and normal. But any new streak or one that’s changing warrants a visit to a dermatologist because early detection makes a significant difference in outcomes.
Signs That Warrant a Professional Look
Most nail bumps are nothing to worry about, but certain patterns deserve attention. A new dark streak that’s widening or changing color. A nail that lifts off the bed without obvious trauma. Redness, swelling, or pus around the nail fold. A nail turning greenish-black, which can signal a bacterial infection. Nails that thicken and stop growing entirely, sometimes associated with internal conditions. Nails that curve downward and feel spongy when pressed, known as clubbing, which can reflect heart or lung problems.
If your bump showed up after an illness or injury and the nail is otherwise a normal color and texture, you can safely wait for it to grow out. If it’s been present for more than six months without improvement, is painful, changes color, or appears on multiple nails without an obvious cause, a dermatologist can examine the nail and, if needed, take a small sample or biopsy to identify what’s going on beneath the surface.