Splinter hemorrhages are tiny streaks of blood trapped beneath your fingernails or toenails. They look like thin, dark lines running lengthwise along the nail, resembling a splinter stuck under the surface. Most of the time they result from minor trauma to the nail and are completely harmless, but in some cases they signal an underlying health condition worth investigating.
What They Look Like
A splinter hemorrhage appears as a narrow, reddish-brown or dark red line that runs in the same direction your nail grows. The lines form because the tiny blood vessels beneath your nail run lengthwise along the nail bed. When one of these vessels breaks, blood leaks into the narrow channel and gets trapped, creating that characteristic thin streak rather than a round bruise. Over time the color may darken to brown or near-black as the blood ages.
You might see a single line on one nail or several lines across multiple nails. The number and location matter, as explained below.
Location on the Nail Matters
Where a splinter hemorrhage sits on your nail offers a useful clue about its cause. Lines near the tip of the nail, in the outer third, are almost always from everyday trauma: bumping your hand, nail biting, using a cane, or working with your hands. These are the ones most people notice and they rarely indicate anything systemic.
Lines that appear closer to the cuticle, in the inner portion of the nail near where it grows out, are more clinically significant. These proximal hemorrhages tend to show up on multiple nails at once and are more commonly linked to infections, blood vessel inflammation, or other systemic conditions. If you notice new lines forming near the base of several nails without any obvious injury, that pattern deserves attention.
Trauma: The Most Common Cause
The vast majority of splinter hemorrhages come from physical injury to the nail. You may not even remember the moment it happened. Slamming a finger in a drawer, gripping tools tightly, playing sports, or even aggressive nail grooming can rupture the delicate capillaries under the nail plate. These trauma-related hemorrhages typically appear on one or two nails, sit near the tip, and grow out with the nail over a few weeks to months. Fingernails grow roughly 3 to 4 millimeters per month, so a hemorrhage near the middle of the nail may take two to three months to reach the free edge and disappear.
Systemic Conditions Linked to Splinter Hemorrhages
When splinter hemorrhages aren’t caused by trauma, they can be a visible clue to something happening deeper in the body. Several categories of disease are known to produce them.
Heart Valve Infections
Splinter hemorrhages have a long historical association with infective endocarditis, an infection of the heart’s inner lining or valves. Bacteria circulating in the bloodstream can damage small vessels, including those under the nails. Before antibiotics were widely available, splinter hemorrhages appeared in 40 to 90 percent of endocarditis cases. Today that number is much lower, around 3 to 5 percent, because infections are caught and treated earlier. Still, between 15 and 33 percent of people diagnosed with endocarditis have splinter hemorrhages at some point during their illness. Endocarditis typically comes with fever, fatigue, night sweats, and sometimes new heart murmurs, so isolated nail lines without other symptoms are unlikely to point here.
Skin and Autoimmune Conditions
Psoriasis and lichen planus are the two skin conditions most commonly linked to splinter hemorrhages. Both involve inflammation that can reach the nail bed. Up to 35 percent of people with lichen planus report having them. Autoimmune conditions that inflame blood vessels, a process called vasculitis, can also be responsible. Lupus and antiphospholipid syndrome both fall into this category. Chronic kidney disease is another association, likely because of the vascular changes that accompany it over time.
Infections Beyond Endocarditis
Any bloodstream infection that causes widespread inflammation of small blood vessels can trigger splinter hemorrhages. Meningococcemia and other bacterial infections that spread through the blood are known causes. Even localized infections near the nail, including fungal nail infections and herpes zoster (shingles) affecting the fingers, have been documented as triggers.
Medications That Cause Them
Certain drugs are strongly associated with splinter hemorrhages. The most notable are cancer-targeting drugs called kinase inhibitors, which work by blocking the growth of new blood vessels. Because these same vessels are needed to repair normal wear-and-tear damage under the nail, the drugs leave the nail bed vulnerable. Between 60 and 70 percent of people taking these medications develop splinter hemorrhages.
Blood thinners also increase the risk. Aspirin, warfarin, and newer anticoagulants all make it easier for tiny nail bed vessels to bleed and harder for the bleeding to stop. Less commonly, certain antibiotics and even some sedatives have been reported to cause them. One case report documented splinter hemorrhages across all ten fingernails after just one week on an antibiotic called nitrofurantoin, which highlights how quickly drug-related changes can appear.
How They Differ From Nail Melanoma
A dark streak under the nail can understandably raise concerns about melanoma. The two can look similar at first glance, but there are key differences. Splinter hemorrhages tend to be reddish-brown, have clear borders, and fade in color from the center outward. They move with the nail as it grows, shifting toward the tip over weeks. Under magnification, they lack any blue or white structures.
Melanoma under the nail, by contrast, typically appears as a brown or black vertical band that stays in the same position because the pigment is being produced continuously at the nail root. The band may widen over time, and the skin around the cuticle can develop dark pigmentation. A splinter hemorrhage that grows out and disappears is almost certainly benign. A dark line that persists in the same spot, changes width, or is accompanied by nail distortion warrants evaluation by a dermatologist, who can examine the nail with a magnifying tool called a dermoscope to distinguish between the two.
When Splinter Hemorrhages Are Worth Investigating
A single splinter hemorrhage on one nail, especially near the tip, is rarely a cause for concern. The picture changes when you see several of these lines appearing on multiple nails at the same time, particularly near the cuticle, with no history of injury. That pattern suggests something systemic is at work.
Context matters most. Splinter hemorrhages accompanied by fever, unexplained weight loss, joint pain, skin rashes, or fatigue point toward an underlying condition that needs evaluation. If you’ve recently started a new medication and notice lines appearing across several nails, the drug is a likely explanation. And if you already have a diagnosed condition like psoriasis, lupus, or kidney disease, splinter hemorrhages may simply be part of that picture rather than a new problem.
On their own, splinter hemorrhages don’t require treatment. They grow out with the nail and disappear. The goal is always to identify and address whatever caused them, whether that means avoiding repetitive nail trauma, adjusting a medication, or investigating an underlying condition.