Category: Surgical Oncology & Dermatology
Dark Nail Lines That Won’t Fade — Chemo Side Effect or Subungual Melanoma Warning?
Red flags — see dermatology or your oncology team promptly
- Single nail — dark line not fading unlike other chemo-affected nails
- Band wider than 3 mm — widening or irregular edges
- Hutchinson sign — pigment on cuticle or periungual skin
- Not migrating with nail growth — band stays fixed even when new proximal nail is clear
- Irregular border/colors — multiple shades in one band (black, dark brown, light brown)
Do not wait a full nail cycle — arrange dermoscopy and possible biopsy
Most dark nail lines after chemotherapy come from temporary pigment stimulation
(chemo-induced hyperpigmentation),
which gradually moves out with nail growth over 6–12 months.
However, if a dark line affects only one nail, does not advance distally, is wider than 3 mm,
or spills onto the cuticle
(Hutchinson’s sign),
see a dermatologist for dermoscopy to rule out
subungual melanoma.
1. Understanding longitudinal melanonychia
Longitudinal melanonychia is a brown or black band running the length of the nail,
caused by increased melanin from melanocytes in the nail matrix.
Causes range from benign (matrix nevus, drugs, trauma) to malignant
(subungual melanoma).
Common causes
- Drugs/chemotherapy: taxanes, anthracyclines, alkylating agents, platinum compounds
- Trauma / onychotillomania: repeated matrix injury
- Nail matrix nevus: usually benign but must be distinguished from melanoma
- Ethnic melanonychia: common in Asian/darker skin — often multiple nails, symmetric
- Subungual melanoma: rare but serious — early detection matters
2. Why chemo can darken nails or create lines
Several chemotherapy classes affect rapidly dividing cells, including melanocytes at the nail base,
causing hyperpigmentation of the whole nail or longitudinal bands — a form of
nail toxicity during systemic anticancer treatment.
Features suggesting a chemo-related cause
- Multiple nails at once — hands and/or feet
- Pigment moves distally — clear new proximal nail pushes old band toward the tip
- Onset after chemo cycles — appears or darkens during treatment
- Fades after stopping — often 6–12 months (~3 mm nail growth per month)
treatment readiness guide
and use the urgency score below.
3. The ABCDEF rule for subungual melanoma warning signs
The ABCDEF mnemonic helps screen
subungual melanoma
— not a diagnosis, but a reason for dermoscopy referral.
- A — Age / Race: more common age 50–70 and in Asian/darker skin (but any age possible)
- B — Band (width/Border): band wider than 3 mm, blurred or irregular edge
- C — Change: darker, wider, or not moving with nail growth
- D — Digit: usually one nail — thumb or big toe common
- E — Extension: Hutchinson sign — pigment on cuticle or nail fold
- F — Family history: melanoma or skin cancer in relatives
4. What is Hutchinson sign? A critical clue
Hutchinson sign means pigment from the subungual band spreads onto the
proximal/lateral nail fold or cuticle — not just under the nail plate.
It correlates with
invasive subungual melanoma
more than benign longitudinal melanonychia.
Versus pseudo-Hutchinson
Nail color or groove shadow can mimic spillover — dermoscopy distinguishes
true Hutchinson (epidermal pigment around the matrix) from optical illusion.
Pigment on cuticle or periungual skin → dermatology within 1–2 weeks; do not wait for nail growth
5. Dermatology workup: dermoscopy & biopsy
- History + exam: duration, chemo drugs, trauma, number of nails, changes
- Nail dermoscopy (onychoscopy): pigment pattern, borders, Hutchinson, vessels
- Serial photos: compare every 1–3 months if borderline
- Matrix biopsy: when suspicious — punch/excision per dermatologic surgeon plan
- Pathology + staging: if melanoma — oncology referral per
NCI guidance
Home monitoring: photos every 2–4 weeks
Use your phone, consistent light and angle, reference the cuticle —
clear new nail plus band moving to the tip suggests benign migration;
a static or widening band needs medical review.
Unsure if this is “normal during treatment” or “needs urgent attention”?
Analyze severity and receive personalized guidance from our Advisory team.
Differential diagnosis of dark lines on nails
| Cause | Line appearance | Number of nails | Change with nail growth | Risk level |
|---|---|---|---|---|
| Chemo-induced hyperpigmentation | Longitudinal band or whole nail, brown–black, even | Usually multiple | Migrates distally, fades ~6–12 months | Low (drug effect) — report if onycholysis/pain |
| Splinter hemorrhage | Short red-brown splinter-like vertical lines | Often 1–2 after trauma | Moves out, resolves in 2–3 months | Low — review if no trauma or recurrent |
| Nail matrix nevus / benign melanonychia | Narrow band <3 mm, uniform color, sharp edge | Often single, stable years | Migrates, does not widen | Low–moderate — dermoscopy if unsure |
| Ethnic / physiologic melanonychia | Narrow brown bands, similar on several nails | Multiple, usually hands | Stable, slow change | Low — watch lone changing nail |
| Subungual melanoma | Band >3 mm, multicolor, irregular ± Hutchinson | Almost always single nail | No migration / widens / darkens | High — dermoscopy + biopsy promptly |
ABCDEF checklist for subungual melanoma assessment
| Criterion | What to look for | Benign signal | Malignant signal |
|---|---|---|---|
| A — Age / Race | Age, ethnicity, family history | Child/teen + narrow stable band (still rule out if unsure) | Over 50, new change, or family melanoma |
| B — Band / Border | Band width and edge clarity | <3 mm, sharp edge, uniform color | >3 mm, blurred edge, multiple colors |
| C — Change | Change over 2–4 weeks | Migrates distally, no widening | Fixed, darker, wider |
| D — Digit | Which finger/toe | Multiple symmetric nails (chemo/ethnic) | Single nail, often thumb/big toe |
| E — Extension (Hutchinson) | Pigment on cuticle/fold | No periungual pigment | Clear Hutchinson sign |
| F — Family history | Melanoma / atypical nevi | No relevant history | Melanoma or syndrome in family |
Frequently asked questions (FAQ)
What causes dark nail lines after chemo, and how long until they fade?
Chemotherapy temporarily stimulates matrix melanocytes, often on multiple nails.
After stopping, pigment moves distally and fades in about 6–12 months.
What does subungual melanoma look like compared with ordinary dark lines?
Usually one nail, band wider than 3 mm, multiple colors, irregular border, no distal migration, possible Hutchinson sign —
unlike chemo bands on several nails that move with growth.
What is Hutchinson sign on the nail, and why does it matter?
Pigment spills onto cuticle or periungual skin, suggesting melanoma spread —
needs dermoscopy and possible biopsy.
When should I see a dermatologist for dermoscopy if dark lines won’t go away?
Single nail, band over 3 mm, no migration, Hutchinson sign, or change in 2–4 weeks — do not wait six months.
How should I photograph nails to monitor dark lines?
Every 2–4 weeks, same light and angle, reference cuticle — clear proximal nail plus band moving distally is reassuring;
a fixed band needs review.
How is splinter hemorrhage different from chemo-related dark lines?
Short splinter-like lines after trauma, moving out in 2–3 months —
not a wide longitudinal band and no Hutchinson sign.
Which chemo drug classes commonly darken nails?
Taxanes, anthracyclines, alkylating agents, platinum compounds — temporary hyperpigmentation, not subungual melanoma.
Is a nail matrix nevus dangerous?
Usually benign but must be distinguished by dermoscopy — biopsy if it changes, widens, or shows Hutchinson sign.
Scientific mechanism (brief)
Nail pigment comes from melanocytes in the nail matrix synthesizing melanin
incorporated into the nail plate during keratinization.
Chemotherapy (especially taxanes and anthracyclines) can transiently activate melanocytes
or alter keratinocyte turnover → longitudinal bands that migrate distally after treatment stops.
In subungual melanoma, atypical melanocytes proliferate in the matrix
and may invade the nail bed and periungual skin (Hutchinson) —
early onychoscopy assesses pigment microstructure and vascular patterns
before matrix biopsy per dermatologic oncology pathways.
Synthesized by
Asst. Prof. Dr. Norawit Raatpiboon
Related reading — oncology cluster
Academic references (E-E-A-T)
- NCI — Melanoma Treatment (PDQ)
- NCI — Skin Cancer
- PubMed — Subungual melanoma: an update (PMID 25905143)
- PubMed — Longitudinal melanonychia in children (PMID 25776751)
- PubMed — Hutchinson sign in melanoma (PMID 29412742)
- PubMed — Nail toxicity from systemic anticancer treatment (PMID 24838785)
Medical disclaimer
This article is for education on dark nail lines and separating chemo effects from suspicious subungual findings only.
It does not replace dermatology exam, dermoscopy, or biopsy.
All decisions belong with your treating physicians and oncology team.
Hutchinson sign, a single rapidly changing nail, or periungual pigment spill requires prompt medical evaluation.