A small black line that forms vertically underneath your nail may be a splinter hemorrhage, while horizontal lines may be melanonychia. These may be harmless or a sign of a more serious health condition.
As the name suggests, splinter hemorrhages look like a wood splinter under your nail. These result from damage to small blood vessels underneath your nail. Characteristics include the following:
- It’s black or reddish brown in color.
- It doesn’t change appearance when you apply pressure to the nail.
- It appears in one or more places under your nail.
Splinter hemorrhages do not typically run across the entire nail. Narrow black lines that start in the nail bed and extend across the entire nail are often the result of melanonychia. This condition occurs due to increased melanin deposits in the nail or changes in the nail pigmentation.
Thicker lines that create a horizontal stripe on the nail are called Beau lines. These are usually not harmful, but nail discoloration in the nail bed
This article discusses the different types of nail lines.
Black lines on the nail can be the result of many conditions.
Splinter hemorrhage causes
Common causes of splinter hemorrhages include:
- Trauma: Trauma is one of the most common causes of splinter hemorrhages. This can occur when something hurts your nail bed and bursts a blood vessel under it.
- Endocarditis: Endocarditis is a heart condition that
may cause splinter hemorrhages. It occurs when the inner chambers or valves of the heart have an infection. - Psoriasis: Psoriasis may also cause splinter hemorrhages. Changes to the nails are a common early symptom of psoriasis but are often overlooked.
Learn more about psoriasis and the nails here.
Less common causes of splinter hemorrhages vary and may include:
- infection
- vasculitis
- lupus
- nail fungus
- lichen planus
- medications that alter blood clotting
- Raynaud’s disease
- kidney, lung, or circulatory diseases
- chemotherapy
Causes of melanonychia
Melanonychia can occur for one of two reasons.
- Melanocytic hyperplasia: Growth in or around the nail can increase the number of pigment cells in the nail bed. As the nail grows, this can cause a dark line to extend the length of the nail. These growths can have benign or cancerous causes.
- Melanocytic activation: This is an increase of melanin deposits in the nail but not of pigment cells.
Melanocytic hyperplasia is the result of atypical growths in the nail bed. These growths may result from:
- cancer
- moles
- lesions
Common causes of melanocytic activation include:
- trauma
- nutritional deficiency
- pregnancy
- psoriasis
- infection
Learn more about the symptoms and causes of melanonychia here.
Beau line causes
Beau lines appear horizontally on the nail and occur when nail growth is interrupted or altered in the nail bed. Common causes of Beau lines include infection of the nail bed or injury from impacts or picking.
However, multiple Beau lines can be a symptom of multiple chronic conditions, including:
- kidney failure
- thyroid disease
- mumps
- melanoma
- diabetes
- syphilis
- chemotherapy side effects
- endocarditis
- pneumonia
Contact your doctor if you’re sure a black line on your nail wasn’t due to trauma or it occurs alongside other seemingly unrelated symptoms.
For example, if you have endocarditis, you may experience symptoms like fatigue, a fever, pale skin, joint pain, and shortness of breath, among others. Psoriasis may appear as a rash, patches, or scales on your skin, particularly on your scalp, face, hands, feet, and skin folds.
When you see your doctor, expect them to take a medical history and perform a physical exam. Your doctor may recommend further testing after your appointment if an underlying condition is suspected.
Treatment of nail discoloration will vary based on the underlying cause of the condition. In some cases, you
The health conditions causing splinter hemorrhages, melanonychia, and Beau lines can vary, so treatment will depend on the underlying cause.
For example, endocarditis requires antibiotics and possibly surgery. Psoriasis is a lifelong condition that requires various topical and oral treatments as well as prevention strategies.
What deficiency causes black lines on nails?
Dark lines in your nails can be caused by not enough protein, vitamin B12, B9 (folate) or vitamin D.
How do I know if my nail line is melanoma?
Stage 1 nail melanoma can look like a streak or band on your nail, often on the thumb or big toe of your dominant hand or foot.
If the skin around the nail is darkened, the melanoma could be more advanced. It is also possible for the nail to split or begin separating from the nail bed.
Can a black line on my nail be a fungus?
While this is less common than other causes, a fungal infection
Nails can be an indicator of your overall health. If you experience splinter hemorrhages, melanonychia, or other nail conditions without a reasonable explanation, it may be a sign that you should see your doctor.
These lines of the nail may be harmless, or they may be a sign of a more serious health condition. If you can recall a trauma to the nail, it’s likely the splinter hemorrhage will grow out with time. If you experience symptoms besides the nail condition, you should see your doctor for a thorough examination and diagnosis.
