Splinter Hemorrhages: What Do Black Lines on Nails Mean?

Do you ever notice black lines running down your nails? While they may seem harmless, these lines sometimes hint at underlying health issues. Your nails reflect more than just grooming habits—they can provide clues about your overall health. Changes in nail color, texture, or markings may be linked to injury, nutritional deficiencies, or systemic diseases. 

One common nail change is splinter hemorrhages, which appear as thin, dark streaks under the nail. This article explores what black lines on nails signify, their causes, and how to address them effectively.

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What Are Black Lines on Nails (Splinter Hemorrhages)?

Splinter hemorrhages are small, thin, black, or dark red lines that appear under the nails. They look like splinters trapped beneath the nail and run in the direction of nail growth. These lines form when tiny blood vessels under the nail burst, causing bleeding that gets trapped in the nail bed.

Types of Black Lines on Nails

Not all black lines under the nails are the same. Here are some distinctions:

Thin vs. Thick Lines‍

Some are thin and straight, resembling tiny splinters, while others are thicker and more irregular. While thick, uneven streaks may sometimes be linked to conditions such as melanoma, they can also result from other causes. A healthcare provider can assess nail changes for an accurate diagnosis.

Associated Conditions‍

Thin lines often result from minor injuries, while thicker lines can be linked to more severe health issues. Understanding the type of line can help identify its cause.

Common Causes of Black Lines on Nails

Black lines on nails can develop for various reasons, ranging from minor external factors to more serious medical conditions. Some causes are harmless and temporary, while others may require medical attention. 

Non-Worrisome Causes

• Nail Injuries: Bumping or hitting your nail can break small blood vessels, creating black lines. This is common in athletes or people who work with their hands.
• Manicures: Frequent manicures or application of artificial nails, where excessive pressure or improper nail tools can cause micro-injuries and bleeding.  
• Tight shoes: Wearing tight shoes can squeeze the toenails and damage small blood vessels.    

Medical Causes

The following medical causes may contribute as well:

Infections

Certain infections can cause splinter hemorrhages. Examples:

• Endocarditis: This is typically seen in individuals with predisposing risk factors, such as heart valve disease.
• Fungal infections: These may also lead to discoloration, nail thickening, and brittleness alongside dark streaks.

Systemic Conditions

Certain health conditions may affect blood flow or cause inflammation, leading to bleeding under the nail. Examples:

• Psoriasis: This autoimmune condition can affect skin and nails, resulting in pitting, thickening, and splinter hemorrhages.
• Vasculitis: Inflammation of blood vessels can cause tiny blood leaks under the nails, appearing as dark streaks.
• Anemia: Low iron levels can make nails more fragile and prone to damage, increasing the likelihood of black lines.

Serious Conditions

A black line can be a sign of melanoma in rare cases. 

• A dark, thick, or expanding black line under the nail—especially one that does not move as the nail grows—may be a sign of subungual melanoma.
• Unlike injury-related lines, melanoma-related streaks often appear in a single nail, may widen over time, and can extend into the surrounding skin.

If black lines on your nails persist, change in size, or appear with other symptoms like pain, swelling, or nail detachment, it's important to consult a healthcare provider for evaluation.

Role of Lifestyle Factors

Lifestyle choices can significantly affect nail health, influencing the likelihood of developing black lines under the nails. Two key factors to consider are nutritional deficiencies and medications.

Nutritional Deficiencies‍

Low levels of Vitamin B12 or iron can weaken nails, making them more prone to damage and bleeding.

Medications‍

Some medications may contribute to splinter hemorrhages in individuals prone to vascular fragility or clotting changes. Consult a healthcare provider for concerns about medication-related nail changes.

• Blood Thinners: Medications that prevent blood clotting can make blood vessels more fragile and prone to bleeding.  Examples include: Warfarin (Coumadin), aspirin, clopidogrel (Plavix), and heparin.  
• Chemotherapy: Certain cancer medications can weaken blood vessels or affect platelet function. Splinter hemorrhages typically develop during the first few weeks of chemotherapy and subside over time.
• Antibiotics and Antiviral Medications: Some antibiotics and antiviral drugs, especially those that impact blood clotting or cause vascular inflammation, can contribute to splinter hemorrhages. Examples include rifampin and interferons.
• Steroids: Long-term use of corticosteroids can weaken and thin blood vessels and tissues, making them more prone to damage and splinter hemorrhages. Examples include prednisone and dexamethasone.
• Immunosuppressants and Autoimmune Medications: Some drugs that treat autoimmune conditions can interfere with blood vessel health. Examples include: methotrexate and biologic therapies (TNF inhibitors).

When to Seek Medical Advice

Knowing when to seek medical advice is crucial, as some black lines on the nails may indicate an underlying health issue. Attention to specific warning signs, such as persistent discoloration or accompanying symptoms, can help determine whether a doctor's visit is necessary.

Warning Signs

• Persistent black lines that don’t go away or spread.
• Accompanying symptoms like pain, swelling, or nail detachment.
• Multiple black lines that appear without injury.

If you notice persistent black lines that do not grow out, lines that widen over time, or are accompanied by pain, swelling, or additional symptoms, consult a healthcare provider for further evaluation.

Diagnostic Process

Evaluation begins with a physical exam and medical history.  Your healthcare provider will examine the nails for size, color, and distribution of the splinter hemorrhages. They may ask about recent injuries, medications, medical history, and additional symptoms (e.g., fever, fatigue, joint pain).

If nail changes are unexplained, persistent, or associated with other symptoms, a healthcare provider may recommend additional tests to rule out underlying health conditions.

Blood Tests

• Complete Blood Count (CBC): Abnormal results may indicate conditions like endocarditis, vasculitis, or leukemia.
• Coagulation Tests: Evaluate how well the blood clots and whether a bleeding disorder or blood-thinning medication is a factor.
• Inflammatory and Autoimmune Markers: Elevated levels suggest systemic inflammation linked to conditions like vasculitis or lupus.
• Iron panel and ferritin levels: to check for iron deficiency anemia.
• Vitamin B12 levels: to rule out B12 deficiency, which can lead to fragile blood vessels and splinter hemorrhages.

Imaging and Heart Tests 

• Echocardiogram (Heart Ultrasound): If infective endocarditis is suspected, an echocardiogram may be done to check for heart valve infections that could cause splinter hemorrhages.

Nail Biopsy 

• If melanoma is suspected, a biopsy of the nail bed may be performed to check for cancerous cells.

Treatment Options for Black Lines on Nails

Whether the lines result from an injury, an infection, or a systemic condition, treating the root issue is essential for restoring nail health and preventing recurrence.

Addressing the Underlying Cause

• Treat Infections or Injuries: Antibiotics or antifungal medications may be prescribed if an infection is causing the black lines. Injuries usually heal on their own over time.
• Manage Systemic Conditions: Conditions like psoriasis or anemia need targeted treatments, which could include medication or dietary changes.

Preventative Care

Tips for healthy nails:

• Eat a balanced diet rich in vitamins and minerals.
• Keep nails trimmed and clean.
• Avoid tight or ill-fitting shoes. 
• Avoid harsh manicures and artificial nails.

Supplements and Topical Treatments‍

Using nail-strengthening creams or taking supplements like biotin may support nail health. Consult a healthcare provider before starting any new supplements.

Understanding the causes and taking steps to prevent black lines under your nails can keep your nails healthy and strong. Consult a healthcare professional for proper diagnosis and treatment if you notice persistent or worsening lines.

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Key Takeaways

• Black lines on nails, known as splinter hemorrhages, can result from minor injuries or indicate underlying health conditions.
• Thin, straight lines are often harmless, while thicker, irregular streaks may require medical evaluation.
• Common causes include trauma, infections, nutritional deficiencies, and systemic diseases like psoriasis or endocarditis.
• Certain medications, such as blood thinners and chemotherapy drugs, can increase the risk of splinter hemorrhages.
• Seek medical advice if black lines persist, spread, or are accompanied by pain, swelling, or other symptoms.
• Treatment focuses on addressing the root cause through lifestyle changes, medical treatment, or proper nail care.
• Preventative measures include maintaining a balanced diet, protecting nails from trauma, and monitoring any nail changes over time.