Black spots on nails: causes and treatment

"Black spots on the nails" is not a diagnosis, but a visual symptom. The most common causes are: subungual bruising following microtrauma, longitudinal melanonychia (pigmented streak), the rare but dangerous melanoma of the nail apparatus, as well as nail staining caused by microbial pigments or exogenous substances. The appropriate treatment depends on correct recognition: in some cases, observation is sufficient, while in others, delay is dangerous. [1]

A bruise under the nail typically darkens from purple-burgundy to black and "moves" toward the free edge as the nail grows. Melanonychia appears as a vertical brown-black streak from the lunula to the edge; it can be benign but can mask early melanoma. Bacterial pigmentation, most often caused by Pseudomonas aeruginosa, produces a greenish-black tint, often on moist nails. [2]

Nail melanoma is rare, but it should not be overlooked. It is characterized by an expanding dark streak with jagged edges, color variations, and Hutchinson's sign—a "flow" of pigment into the nail folds. In adults with a single, newly developed dark streak on the thumb or toe, a matrix biopsy should always be considered. [3]

This article provides a step-by-step, practical algorithm: how to distinguish safe from dangerous causes, what tests to take, when to urgently see a dermatologist/oncologist, and how to treat each situation. Separate sections are devoted to ICD-10/ICD-11 codes, epidemiology, risk factors, and modern treatment methods, including new and gentle approaches. [4]

Code according to ICD-10 and ICD-11

Codes depend on the cause. For melanoma of the skin of the nail apparatus, ICD-10 uses C43.* with an indication of the region: upper limb (C43.6, with lateralization in subheadings), lower limb (C43.7), and for melanoma in situ - the D03.* series (e.g., D03.6/D03.7). Benign changes in the nails, including melanonychia without a tumor, are more often coded in block L60 "Diseases of the nails" (e.g., L60.8 "Other diseases of the nails"). Subungual bruise after trauma can be coded as superficial injury/hemorrhage of the finger area according to chapter S60 with clarifications. [5]

In ICD-11, cutaneous melanoma is classified in block 2C30 (with the subtype acral lentiginous melanoma 2C30.3), and melanoma in situ is classified in 2E63.*. For non-neoplastic "black spots," terms from the sections on nail diseases and injuries are used; ICD-11 makes extensive use of post-coordination (specific localization—"nail apparatus" of the upper or lower limb, side, degree, etc.). This helps to more accurately pinpoint the locus (thumb/thumb), which is important for routing and statistics. [6]

Table 1. Frequently used codes for "black spots on nails"

Clinical situation	ICD-10 (examples)	ICD-11 (examples)
Melanoma of the nail apparatus (upper limb)	C43.6 (+ subheading by side)	2C30 (clarification: acral-lentiginous; localization: nail apparatus of the hand)
Melanoma of the nail apparatus (lower limb)	C43.7	2C30 (localization: nail apparatus of the foot)
Melanoma in situ	D03.6/D03.7	2E63.*
Benign melanonychia/other nail diseases	L60.8	nail disease block with post-coordination
Subungual bruise (trauma)	Chapter S60 with clarifications	chapter on injuries with clarification of the area and side

Sources: official codes and reference books. [7]

Epidemiology

Subungual hemorrhages are the most common "black" scenario among active individuals, runners, and those with household microtraumas. Precise population percentages are rare, but they are a common finding in general practice and dermatology. Green-black discoloration associated with Pseudomonas aeruginosa infection is also quite common among people with wet hands, during pool sanitation, and in those who enjoy prolonged application of "dense" coatings. [8]

Longitudinal melanonychia is common and is more often observed in people with a dark phototype; often, multiple stripes are present, affecting several fingers at once—a benign, "ethnic" phenomenon. Drug-induced melanonychia occurs in association with certain chemotherapy drugs, hydroxyurea, and other medications, which is important to consider when collecting the patient's medical history. [9]

Nail melanoma is a rare form, accounting for approximately 0.7-3.5% of all melanomas in the general population and up to 2-3% in fair-skinned individuals. The big toe and thumb are most commonly affected; incidence is highest in those aged 50-70 years, but it also occurs in younger individuals. This rarity is coupled with diagnostic delays, which worsens the prognosis. [10]

The rate of "false positive" alarms is high: most dark streaks in adolescents and young adults are benign. However, a single new streak in an adult, especially one that is expanding and has variable coloration, requires caution and examination. [11]

Table 2. What is most common?

Cause	Relative frequency in practice
Subungual bruise after microtrauma	Very often
Benign melanonychia (including "ethnic", drug-induced)	Often
Pseudomelanonychia (microbial/exogenous staining)	Often
Nail melanoma	Rare (≈0.7-3.5% of all melanomas)

Sources: clinical reviews and dermatological guidelines. [12]

Reasons

Subungual bruising occurs due to impact, shoe pressure, or repeated microtrauma. Blood under the nail plate gives the nail a dark color and "migrates" toward the edge as it grows, which is a key clue that it is a hemorrhage rather than a tumor. Dermoscopy reveals uniform or marbled dark red/black areas and hemorrhagic globules. [13]

Melanonychia is melanin in the lamina. Sources of melanin include activated matrix melanocytes (benign streaks), melanocytic matrix nevus, and, rarely, melanoma. Melanin can also "tint" the lamina due to fungal or inflammatory conditions. Medications (chemotherapy, hydroxyurea, etc.) also cause diffuse or streaky changes. [14]

Pseudomelanonychia is a pigment not derived from melanin: the blackish-greenish tint is caused by pigments from Pseudomonas aeruginosa, while dark spots can also be caused by dyes, nicotine, silver nitrate, henna, and dirt. Such cases are confirmed by partial pigment removal, and dermatoscopy and culture reveal the cause. [15]

Tumors are a dangerous group of causes. Nail melanoma often begins as a narrow dark streak (usually one on one finger), becoming wider, darker, and more irregular over time, and may be accompanied by longitudinal cracks, bleeding, and dystrophy. The spread of pigment to the periungual fold (Hutchinson's sign) is a warning sign. [16]

Risk factors

Bruises can be caused by running, football, tight shoes, traumatic manicures/pedicures, manual labor, and musical instruments. Repeated micro-impacts create a "chronic" hematoma, which can easily be mistaken for melanonychia. Protective footwear and proper nail trimming dramatically reduce the risk. [17]

For benign melanonychia - dark skin phototype, familial tendency to "ethnic" stripes, multi-digit lesions, taking certain medications (chemotherapy drugs, hydroxyurea, etc.). In drug-induced forms, there are several stripes and they are more symmetrical. [18]

For microbial staining, frequent maceration, wet work, prolonged use of occlusive gloves, chronic onycholysis, and long-term application of heavy coatings without ventilation are all factors. Proper nail sanitation and drying reduce the risk. [19]

For melanoma, age over 50, a single new lesion on the thumb/toe, previous trauma as a possible trigger, and a family history of melanoma are all factors. In fair-skinned individuals, the incidence of subungual melanoma is low, but the prognosis is grave if diagnosed late. [20]

Table 3. Risk factors by groups

Group	Examples
Trauma/pressure	Running, football, tight shoes, manicure injuries
Melanin pigment	Dark phototype, medications (hydroxyurea, chemotherapy), matrix nevus
Non-melanin pigment	Pseudomonas, dyes (henna, silver nitrate), nicotine
Tumor risks	Age >50 years, single new band on the thumb, family history

Sources: clinical reviews. [21]

Pathogenesis

In subungual hemorrhage, blood accumulates between the nail bed and the nail plate. Hemoglobin and its breakdown products change color from burgundy to black, then "slide" toward the distal edge. This results in a pathognomonic sign: gradual distal migration of the spot in sync with nail growth. [22]

Melanonychia develops when matrix melanocytes begin to synthesize melanin and "load" it onto the nail keratin. In benign activation, the bands are parallel and monotonous; in neoplastic transformation, variations in color and width, discontinuities in the bands, and a "dirty" background appear. Dermatoscopic criteria help differentiate these scenarios. [23]

Pseudomonas forms a pigment biofilm (pyocyanin, pyoverdin), which produces a greenish-black tint. This superficial process is often associated with onycholysis and responds to topical antimicrobial measures. Unlike melanin, this color is partially removed by cleansing. [24]

Nail melanoma often has an acral-lentiginous morphology, grows from the matrix, early involves the periungual skin (Hutchinson sign), and can destroy the nail plate. Late diagnosis is associated with a worse prognosis, so the algorithm is designed to detect early signs. [25]

Symptoms

Bruise: pain/pressure after a blow or running, a dark spot that gradually moves toward the edge; with a fresh injury - pulsation. Dermoscopy shows uniform dark tones or a "marbled-bloody" pattern. [26]

Benign melanonychia: a thin, even, uniform vertical stripe(s), often on several nails at once, without destruction of the nail and without pigment leakage onto the surrounding skin. The history is long and stable. [27]

Microbial/exogenous pigmentation: greenish-black or dirty-black color, more often on wet/detached nails; some pigment is removed from the surface during cleaning, the odor may be unpleasant. [28]

Melanoma: a single, expanding, dark streak with variable thickness and color, longitudinal fissures, fragility, and pigment "flow" onto the skin folds (Hutchinson sign). Any new streak in an adult, especially on the thumb, requires evaluation. [29]

Classification, forms and stages

Depending on the source of the pigment, a distinction is made between hemorrhagic (blood), melanin (benign/tumor melanonychia), and non-melanin (bacterial/exogenous pigments). This division reflects the pathogenesis and determines the diagnosis. [30]

By distribution - single nail versus multiple nails. Multiple nails more often indicate benign or drug-induced causes; a single streak in an adult is a "red flag." [31]

For melanoma, general oncological staging is used based on tumor thickness and the presence of metastases; for nail cancer, there are no established clinical "substages," but dermatoscopic criteria for malignancy are important. A decision to biopsy is made at the slightest suspicion. [32]

Bruises are conventionally divided into acute (with pain and pressure, decompression is indicated) and old (painless, observation); microbial stains are divided into isolated and combined with onycholysis. This determines the tactics. [33]

Complications and consequences

An untreated large subungual bruise causes severe pain and can lead to secondary nail deformity; decompression relieves the pain and minimizes the risk of complications. For patients with frequent physical activity, correcting footwear and technique is important. [34]

Microbial pigmentation with prolonged maceration maintains onycholysis and an unpleasant odor; without sanitation and nail drying, relapses are inevitable. In rare cases, systemic therapy is required. [35]

The main risk is missing a melanoma. Late presentation means a thicker tumor and a worse prognosis. Therefore, it's better to perform an extra matrix biopsy than to miss an early stage. [36]

Psychological burden is also significant: fear of cancer, cosmetic discomfort. A clear diagnostic plan and explanation of "red flag" signs reduce anxiety and increase adherence to monitoring. [37]

When to see a doctor

Urgent: severe throbbing pain and "tension" under the nail after injury - a reason for decompression; a single new dark streak in an adult; "steps" of the streak widening, "dirty" uneven coloring, pigment coming out onto the skin of the folds (Hutchinson sign). [38]

Scheduled for the next few days: multiple streaks associated with medication use, persistent greenish-black discoloration with wet work, chronic onycholysis. These cases are rarely urgent but require confirmation and treatment. [39]

If the cause is unclear, it's best not to cover the nail with a thick, dark polish—this interferes with observing the progress. A visit to a dermatologist with the possibility of a dermatoscopy (onychoscopy) is the first step. [40]

Any changes in people with a family history of melanoma or a history of melanoma require a lower threshold for biopsy. It is better to obtain a morphological diagnosis once than to observe a suspicious band for a long time. [41]

Diagnostics

Step 1 - Anamnesis and examination: trauma/sport/footwear, medications, duration, one nail or several. Examination includes dermatoscopy: for hemorrhage - uniform/marbled dark tones with "globules", for benign melanonychia - parallel uniform lines, for melanoma - variable lines, different thickness, "dirty" background, Hutchinson's sign. [42]

Step 2 - "migration test": mark the proximal border of the pigment and re-evaluate after 4-6 weeks. Distal displacement indicates a hematoma; lack of displacement with increasing heterogeneity is an alarming sign. [43]

Step 3 - Laboratory testing as indicated: surface culture if Pseudomonas is suspected; scraping/PCR if fungus is suspected, if there is onycholysis and dystrophy. For drug-related causes, laboratory testing is rarely necessary - the drug history is more important. [44]

Step 4 - Invasive diagnostics: If there is any suspicion of oncology, a targeted nail matrix biopsy is performed (sometimes with partial removal of the nail plate). This is the "gold standard" for excluding/confirming nail melanoma. Morphology determines further treatment. [45]

Table 4. Mini-algorithm for interpreting the “black nail”

Sign	Most likely	Action
Pain after impact, the spot "moves" to the edge	Hemorrhage	Observation/trepanation in case of pain
Several thin stripes on many nails	Benign/drug-induced melanonychia	Monitoring, discontinuation/replacement of medication as indicated
Green-black color, wet work	Pseudomonas	Local sanitation/antiseptics, sometimes antibiotics
One widening stripe, "dirty" background, Hutchinson's sign	Melanoma	Urgently see a dermatologist, matrix biopsy

Sources: dermatological guidelines and reviews. [46]

Differential diagnosis

Hemorrhage versus melanonychia: the key is the migration of the spot and its relationship to trauma. With a hematoma, the color fades and shifts over time; with a melanized streak, it remains fixed at the socket and can slowly expand. Dermoscopy and follow-up examination are key. [47]

Melanoma versus benign melanonychia: a single, asymmetrical, heterogeneous streak with a "dirty" background and Hutchinson's sign requires biopsy. Benign streaks are often multifocal, monotonous, and stable. In children and in darker phototypes, benign streaks are often normal. [48]

Pseudomelanonychia versus true melanization: some pigment is removed, an odor is often present, and the nail may detach. Culture/smear and debridement quickly clarify the situation. [49]

Exogenous dyes against pathologies: traces of henna, silver nitrate, nicotine, and dirt cause superficial staining; the "scratch test" and time factor help differentiate. If in doubt, perform a dermatoscopy/re-examination after 2-4 weeks. [50]

Table 5. Dermoscopic clues

State	Findings
Subungual hemorrhage	Homogeneous dark areas, hemorrhagic globules, marbling; dynamics - distal displacement. [51]
Benign melanonychia	Parallel, regular, uniform lines; smooth edges. [52]
Nail melanoma	Irregular lines of varying thickness/color, "dirty" background, Hutchinson's sign. [53]
Pseudomelanonychia	The superficial pigment, sometimes greenish-black, is partially removed; associated onycholysis. [54]

Treatment

A subungual bruise without significant pain may not require treatment: it will "retract" to the edge and disappear as the nail grows. If the pain is severe, a trepanation—microdecompression (puncture/burning through the nail plate with a disposable instrument)—is performed by a doctor to drain the blood. This quickly relieves pressure and pain; the risk of infection with aseptic technique is minimal. Afterward, dryness and protection are recommended, and if playing sports, footwear and technique should be adjusted. [55]

If the bruise is old but covers more than 50-60% of the nail, observation remains standard. It is important to document the border of the bruise and ensure its distal migration. If there is any doubt about the diagnosis or unusual dynamics, repeat the examination with dermatoscopy. Any "abnormal behavior" is a reason to exclude pigmented causes. [56]

For microbial pigmentation caused by Pseudomonas ("green/black-green nails"), the key is to eliminate moisture and biofilm. Regular drying and topical antiseptics are recommended; in persistent cases in adults, short-term systemic therapy (e.g., ciprofloxacin) may be recommended as prescribed by a physician. Onycholysis is also treated in parallel to eliminate the biofilm "pocket." [57]

Exogenous stains are treated by removing the source and gently sanding/cleaning the surface, sometimes with gentle keratolytics for smoothing. Nicotine staining fades as it grows out; henna and silver nitrate gradually wash out. The key is to avoid covering the stain with heavy coverings for months to monitor progress. [58]

Benign melanonychia does not require treatment if its benign nature is confirmed. Treatment is observation with photographic documentation every 3-6 months. In drug-induced melanonychia, discontinuation or replacement of the medication is discussed if possible without compromising the underlying condition. In children and those with darker skin types, the streaks often remain permanent and do not require intervention. [59]

If the band is aesthetically disturbing, gentler options are possible: laser therapy (targeted pigment coagulation) by an experienced specialist or partial removal of the pigmented area of the matrix with gentle refixation. However, any cosmetic interventions on the matrix are risky and can lead to deformities—the decision is strictly individual. [60]

If melanoma is suspected, treatment is surgery with oncological alertness: diagnostic matrix biopsy (sometimes excisional), and if confirmed, excision with margins according to oncologic standards. In the early stages, local treatment is usually sufficient; in the case of invasion/metastases, systemic methods (immunotherapy, targeted therapy) are added according to skin melanoma protocols. Timeliness in this case determines the prognosis. [61]

After nail surgery, rehabilitation includes protecting the finger, preventing infection, and learning how to care for the nail bed and sutures. The cosmetic outcome depends on the extent of the excision; sometimes, reconstruction of the nail bed or folds is required. Quality of life improves with adaptation, and it is important to discuss expectations and alternatives in advance. [62]

For the "gray zone"—a single lesion without obvious malignancy but also without stability—a "low-threshold biopsy" strategy is acceptable. The patient receives a reminder of "red flags" (expansion, darkening, jagged edges, pigment leakage onto the skin, fragility, bleeding). Any of these events is a signal for an expedited biopsy. [63]

In all scenarios, training and photo recording are essential. A series of photos taken at the same angle and lighting, plus a marker at the proximal border, allow for objective monitoring of dynamics over weeks. This will reduce false alarms and, conversely, raise a flag in a timely manner if the band exhibits atypical behavior. [64]

Table 6. Treatment methods: what, when and why

Situation	Method	Target
Painful, sharp bruise	Trepanation (decompression)	Relieve pressure, pain
An old bruise without pain	Observation	Wait for the stain to move away
Pseudomonas	Sanitation, drying, sometimes systemic antibiotics	Destroy biofilm, remove pigment
Exogenous dyes	Source removal, soft sanding/care	Restore appearance
Benign melanonychia	Observation/photography, medication adjustments	Avoid unnecessary procedures
Suspicion of melanoma	Matrix biopsy → oncosurgery	Early diagnosis and treatment

Sources: clinical guidelines and reviews. [65]

Prevention

Injury prevention: wear proper athletic shoes, trim nails to a soft square, not too short, wear socks that fit properly, and change them when they get wet. Runners may find it helpful to test laces and insoles to reduce the impact on the big toe. [66]

For microbial pigmentation: keep nails dry, treat onycholysis, limit prolonged occlusion with gloves, air out nails between manicures, and avoid wearing polish continuously for months. When working in wet conditions, use a cotton lining under gloves. [67]

To prevent observation errors: do not cover suspicious streaks with opaque varnishes, take photographs and monitor them every 4-6 weeks. When taking suspected medications, be aware in advance that streaks are possible and show them to a doctor if they appear. [68]

Oncovigilance: be aware of "red flags" (single new band in an adult, dilation/heterogeneity, Hutchinson's sign, fissures, bleeding). The threshold for biopsy should be low - this saves lives. [69]

Forecast

The prognosis for bruising is good: pain quickly subsides after decompression, and appearance returns to normal as the nail grows. Recurrence is prevented by wearing proper footwear and maintaining proper exercise hygiene. [70]

Pseudomonas staining and exogenous stains respond well to debridement and drying. It is more important to prevent further onycholysis and maceration, otherwise the pigment will return. [71]

Benign melanonychia is usually stable and does not affect health. Patients can be observed without concern if the diagnosis is clear. [72]

Nail melanoma is rare, but the prognosis depends entirely on early detection and tumor thickness at the time of treatment. The earlier the diagnosis, the higher the survival rate and the easier the treatment. [73]

FAQ

The streak appeared after a hammer blow. Is it cancer?
Most likely not. A bruise is characterized by pain/pressure and a "movement" of the spot to the edge. Mark the border and see a doctor if in doubt. [74]

How can you tell if it's a melanoma, not a hematoma?
A hematoma "moves" distally; a melanoma becomes fixed at the socket and expands, giving an uneven color and possibly "extending" onto the skin folds (Hutchinson). If in doubt, consult a dermatologist and, if necessary, perform a biopsy. [75]

Are there multiple stripes on both hands? Is this dangerous?
Most often, this is benign melanonychia (including "ethnic" melanonychia) or a drug effect. However, an initial examination and photo observation are advisable. [76]

My nail has turned green after frequent wet work. What should I do?
Dry it, sanitize it, and treat onycholysis; sometimes a doctor will prescribe a short course of systemic antibiotics. And most importantly, eliminate moisture and "pockets." [77]

Should a nail be removed immediately if melanoma is suspected?
No. A targeted matrix biopsy is performed first to determine morphology. The extent of the surgery is determined based on the results. [78]