The black or brown discoloration of fingernails and toenails, known medically as melanonychia or hyperpigmentation, is a common side effect experienced by individuals undergoing chemotherapy. This change is directly related to the way anti-cancer drugs work, as they target cells that rapidly divide. While the appearance of darkened nails can be alarming, this condition is generally considered cosmetic and resolves with time. Understanding the biological process behind this discoloration can help patients during treatment.
The Biological Cause of Nail Hyperpigmentation
Chemotherapy drugs attack rapidly dividing cancer cells, but they also affect healthy, fast-dividing cells, such as those in the hair, digestive tract lining, and the nail unit. The nail plate is formed by the nail matrix, a specialized area located beneath the cuticle where nail growth originates.
The nail matrix contains melanocytes, the pigment-producing cells that determine skin and hair color. Although usually inactive in the nail matrix, the toxic effect of chemotherapy stimulates them into heightened activity. This stimulation causes melanocytes to produce and deposit excess melanin into the newly forming nail plate. The result is the appearance of dark streaks, bands, or diffuse discoloration in the nail, often brown, black, or blue-black.
The pattern of discoloration corresponds to the specific chemotherapy schedule. Since nails grow slowly—fingernails take about six months and toenails up to eighteen months to grow fully—the pigmented band moves gradually outward over time. This temporary disruption to the melanocytes and the nail growth cycle is the reason for the visible darkening, marking when the drug was administered.
Chemotherapy Drugs Most Likely to Cause Discoloration
The likelihood and severity of nail hyperpigmentation depend on the specific class of chemotherapy drug used, the dosage, and the duration of treatment. Certain anti-cancer agents are frequently implicated in triggering melanonychia.
The most frequently implicated agents are the Taxanes, a class of drugs that includes paclitaxel and docetaxel. Anthracyclines, such as doxorubicin and daunorubicin, are also highly associated with discoloration, often causing diffuse or transverse dark bands. Other cytotoxic agents, including cyclophosphamide and 5-Fluorouracil (5-FU), have been reported to cause similar pigmentary changes. Combining multiple chemotherapy drugs can increase the risk and intensity of discoloration due to an additive toxic effect on the nail matrix.
The hyperpigmentation may appear within a few weeks of starting treatment, coinciding with the time it takes for the affected nail section to emerge from beneath the cuticle. Higher cumulative doses of the medication often correlate with a more pronounced and darker discoloration.
Managing and Monitoring Nail Changes
While nail darkening itself is benign, managing the associated discomfort and monitoring for more serious complications is necessary during chemotherapy. One strategy to mitigate nail damage, particularly with Taxane regimens, is cryotherapy, or “nail icing.” This involves placing frozen gloves or socks on the hands and feet for a period before, during, and after the drug infusion to temporarily constrict blood vessels. This reduced blood flow limits the amount of drug reaching the nail matrix, thereby reducing the toxic effect.
Maintaining meticulous nail hygiene is a basic defense against further complications. Patients should keep their nails trimmed short and filed with smooth edges to prevent snagging or trauma. Moisturizing the cuticles and surrounding skin regularly helps maintain the integrity of the nail unit, which can become dry and brittle during treatment. It is also advisable to wear gloves when performing household chores, such as washing dishes or gardening, to minimize chemical exposure and physical impact.
The discoloration is temporary, and the affected nail will grow out and eventually be clipped away. Patients should immediately consult their oncologist or dermatologist if they notice signs of a more serious condition. Warning signs include significant pain, redness, swelling around the nail folds, or the lifting of the nail plate from the bed, known as onycholysis. These symptoms may indicate a bacterial or fungal infection, requiring prompt medical intervention, especially when the immune system is suppressed during chemotherapy.