Chromonychia
Chromonychia (nail discoloration) is the medical term for any abnormal change in the color of the nail plate, nail bed or the soft tissue around the nail. The change may be nothing more than a localized cosmetic issue, but it can also be a clue to chronic internal disease, heavy-metal poisoning or a systemic infection.
The causes of chromonychia fall into three main groups by origin:
- Endogenous pigmentation from the nail matrix: Melanocytes in the nail matrix produce more melanin, or the matrix accumulates other internally produced substances. The pigment is built directly into the keratin layers of the nail plate as it forms and gradually moves toward the free edge as the nail grows.
- Nail bed and vascular origin: The abnormal color is not in the nail plate itself but comes from the blood vessels beneath it. It results from changes in blood flow, bleeding, new vessel growth, or deposits of proteins or metals (such as copper, silver or bilirubin) in the nail bed. The overlying nail plate remains naturally translucent.
- Exogenous staining: Pigment from the environment (chemicals, nail polish, dyes, plant sap, antiseptics) clings to the outer surface of the nail plate, or microorganisms growing in the space under the nail release colored pigments (the classic example being the blue-green pigment of Pseudomonas).
When we see a patient with chromonychia at Haute-Derma, we always start with two quick in-office checks: gently scraping the nail surface (to rule out external staining) and pressing on the nail plate or tracking how the color moves as the nail grows (to tell whether the pigment lies in the nail plate or the nail bed). Combined with nail dermoscopy (onychoscopy) under polarized light, these steps usually point to the cause without needing an invasive biopsy at the outset.
Clinical Types by Color
Black / Brown Nails (Melanonychia)
- Increased number or activity of melanocytes: Appears as a brown or black band running lengthwise from the proximal nail fold to the free edge (longitudinal melanonychia). It must be distinguished between a benign nail matrix nevus, pigmentation from medication or trauma, and subungual melanoma.
- Subungual hematoma: Caused by a crush injury. The blood starts out reddish-purple and later turns brownish-black. The mark has smooth, rounded edges, is separate from the nail matrix and moves outward as the nail grows.
Green Nails (Chloronychia / Green Nail Syndrome)
- The nail plate turns green, moss green or greenish-black.
- Cause: Infection with the gram-negative bacterium Pseudomonas aeruginosa, which produces two characteristic pigments: pyocyanin (blue) and pyoverdin (fluorescent green). It usually develops on nails that have lifted from the bed (onycholysis) or in people whose hands are wet for long periods.
Red / Pink Nails (Erythronychia)
- Longitudinal erythronychia: A pinkish-red band running along the length of the nail.
- Often caused by benign growths in the nail matrix or nail bed, such as a glomus tumor (known for sharp, intense pain on light touch or exposure to cold) or onychopapilloma, or by nail lichen planus or Darier disease.
Yellow Nails (Xanthonychia)
- Yellow nail syndrome: A rare triad of (1) pale yellow or greenish-gray nails that are thick, hard, overcurved and grow very slowly or stop growing altogether; (2) lymphedema; and (3) chronic respiratory disease (bronchiectasis, chronic sinusitis, pleural effusion).
- Other causes: Fungal nail infection, nail psoriasis, diabetes, or long-term nicotine staining in heavy smokers.
Blue / Purple Nails (Cyanonychia / Blue Nail)
- Wilson disease: An inherited disorder of copper metabolism in which copper deposits in the nail matrix produce a blue lunula.
- Medications and heavy metals: Silver deposits (argyria), antimalarials (chloroquine, hydroxychloroquine) or long-term minocycline.
- Poor circulation / cyanosis: Reduced oxygen saturation in the fingertip capillaries due to congenital heart disease, respiratory failure or Raynaud's phenomenon.
Nail Color Changes at a Glance
| Nail Color | Location of the Change | Common Causes |
|---|---|---|
| Green / Moss green | Space beneath the nail plate | Pseudomonas aeruginosa |
| Longitudinal red band | Nail bed / Nail matrix | Glomus tumor, onychopapilloma |
| Thick yellow | Entire nail plate | Yellow nail syndrome, fungal infection, psoriasis |
| Blue (lunula) | Lunula / Nail matrix | Wilson disease, silver poisoning, chloroquine |
| Longitudinal black / brown | Nail matrix | Nail matrix nevus, subungual melanoma, hematoma |
Diagnosis and Treatment at Haute-Derma
Clinical Diagnostic Steps
- Scrape test: The surface of the nail plate is gently scraped with a scalpel blade. If the color comes off easily, it is external staining (nail polish, chemicals, ink).
- Pressure test: Firm pressure is applied to the nail plate. If the abnormal color fades, the problem lies in the blood vessels of the nail bed (apparent discoloration). If the color stays the same, the pigment is within the nail plate itself.
- Tracking movement with nail growth: The position of the mark relative to the proximal nail fold is recorded with a small notch on the nail plate. If the mark moves toward the free edge over time, it comes from the nail matrix or from trauma-related bleeding. If it stays put, the lesion is fixed in the nail bed (for example, a glomus tumor or an internal medical condition).
Treatment Principles
- Treating chloronychia caused by Pseudomonas: Trim away the lifted part of the nail; soak the nail in 1% acetic acid (diluted vinegar) or povidone-iodine 2–3 times a day; apply topical ciprofloxacin or tobramycin solution. Keeping the fingers dry at all times is essential.
- Longitudinal erythronychia with a suspected glomus tumor: The tumor is surgically removed under an operating microscope to preserve the nail plate, which markedly reduces, and usually resolves, the stabbing pain.
- Longitudinal melanonychia: Onychoscopy is performed for screening. If there are high-risk features for melanoma (a band wider than 3 mm, uneven color, or pigment spreading onto the proximal nail fold – a positive Hutchinson sign), a nail matrix biopsy is mandatory for histopathological diagnosis.
