The observation of thin, red lines underneath the fingernails is medically known as splinter hemorrhages. These streaks are small areas of bleeding that occur beneath the nail plate, named because they often resemble a tiny wood splinter lodged under the nail. While they frequently result from a minor, harmless injury, these hemorrhages can also indicate an underlying systemic health condition requiring evaluation.
Understanding the Appearance of the Lines
Splinter hemorrhages appear as linear streaks running longitudinally in the direction of nail growth, not horizontally across the nail. This orientation occurs because the small capillaries in the nail bed are aligned parallel to the finger. The nail bed is a highly vascular area beneath the nail plate, and when these capillaries rupture, the blood becomes trapped and visible.
The color of the streak indicates its age: fresh hemorrhages appear red, while older, clotted blood may look reddish-brown or nearly black. These streaks are typically small, measuring between 1 to 3 millimeters in length. Since the blood adheres to the nail plate, the mark slowly moves outward toward the tip of the finger as the nail grows.
The location can suggest the cause. Streaks appearing closer to the nail tip are often linked to trauma. In contrast, streaks appearing more proximally (closer to the cuticle) or those affecting multiple nails simultaneously are more likely signs of systemic disease. These streaks should be differentiated from Beau’s lines, which are horizontal depressions in the nail plate itself, not discoloration beneath it.
Causes Related to Physical Impact and Medication
The most frequent cause of splinter hemorrhages is direct physical trauma to the nail. This trauma can range from a single, forceful impact, such as slamming a finger in a door, to repetitive, minor impacts associated with certain occupations or activities. Stubbing a toe or aggressive manicuring practices, including the application of acrylic nails, can also cause the small vessels in the nail bed to rupture.
In these cases, the hemorrhages are typically harmless, painless, and localized to the injured finger or toe. The mark will resolve naturally as the nail grows out over the course of several weeks to a few months. No specific treatment is necessary for trauma-induced hemorrhages, as the body heals the tiny rupture on its own.
Certain medications can also increase the likelihood of developing these streaks as a side effect. Drugs that thin the blood, such as aspirin or warfarin, may cause bleeding in the nail bed capillaries. Additionally, some chemotherapy agents, particularly tyrosine kinase inhibitors, are known to cause splinter hemorrhages in a high percentage of patients. These drug-related hemorrhages often affect multiple nails and may resolve after the medication is discontinued or the dosage is adjusted.
Underlying Systemic Health Conditions
When splinter hemorrhages appear without a history of trauma, or in multiple digits, they can indicate a more serious underlying systemic health condition. These diseases often involve damage to the body’s small blood vessels, either through inflammation or the formation of tiny blood clots. The most well-known association is with infective endocarditis, a severe bacterial infection of the heart’s inner lining or valves.
In endocarditis, clumps of bacteria and cellular debris, known as septic emboli, break off from the infected heart valve and travel through the bloodstream. When these micro-emboli reach the small capillaries beneath the nail, they lodge there, causing vessel damage and rupture. These hemorrhages are considered a classic, though often late, sign of this condition.
Inflammation of the blood vessels, or vasculitis, is another mechanism leading to splinter hemorrhages. Systemic autoimmune conditions, such as Systemic Lupus Erythematosus (SLE) and Rheumatoid Arthritis, cause this inflammation, making nail bed capillaries fragile and prone to bleeding. In these conditions, the hemorrhages result from injury to the vessel walls, often alongside other symptoms like joint pain or rashes.
Psoriasis, a common skin condition, can also affect the nail bed, making it susceptible to hemorrhage. Conditions that affect clotting and circulation, such as chronic kidney disease or antiphospholipid syndrome, are also linked to the formation of these streaks.
When to Seek Medical Consultation and Evaluation
A single splinter hemorrhage traceable to a specific injury is generally not a cause for immediate concern and can be safely monitored. Medical consultation becomes advisable when the cause is unknown, or if the streaks appear on multiple fingers or toes without any history of trauma. Persistent hemorrhages that do not grow out with the nail or those that recur frequently should also prompt a visit to a healthcare provider.
It is important to seek prompt medical attention if the hemorrhages are accompanied by other systemic symptoms. These signs include an unexplained fever, joint pain, shortness of breath, a general feeling of illness, or the appearance of tiny red dots on the skin known as petechiae. These combined symptoms suggest the possibility of a serious systemic condition, such as infective endocarditis.
A physician will typically begin the evaluation with a detailed physical exam and a review of the patient’s medical history and current medications. If a systemic cause is suspected, diagnostic tests may be ordered to investigate the possibility of infection or inflammation. Common tests include:
- A complete blood count.
- Blood cultures to detect bacteria.
- Tests to measure inflammation levels.
- Imaging tests, such as an echocardiogram, to evaluate the heart valves for signs of infection.