Toenail discoloration, known medically as chromonychia, is a common symptom indicating a change within the nail unit or reflecting an internal shift in the body. The nail unit consists of the translucent nail plate, made of hardened keratin, resting on the underlying nail bed. The color of a healthy nail is primarily derived from the blood vessels visible through the nail plate. Discoloration occurs when the nail plate is stained, the nail bed is damaged, or the body’s internal chemistry is altered.
Fungal Infections (Onychomycosis)
The most frequent cause of toenail discoloration is a fungal infection, termed onychomycosis. This infection is commonly caused by dermatophytes, fungi that feed on the keratin protein of the nail. The appearance typically includes thickening and crumbling of the nail plate, often beginning at the tip and sides.
The color of the infected nail can vary widely, most often presenting as yellow, white, or brown. In some cases, the presence of molds or yeasts can lead to a greenish or black hue. Because the fungi thrive in warm, moist environments, the discoloration and structural damage spread slowly as the infection progresses.
Physical Trauma and External Causes
Discoloration can result directly from physical injury. Trauma, such as dropping a heavy object or repetitive microtrauma from ill-fitting athletic shoes, can cause bleeding underneath the nail plate. This results in a subungual hematoma, where blood pools between the nail plate and the nail bed, causing a dark red, purple, or black spot.
This black or deep purple coloring is a bruise that will gradually grow out with the nail over several months. External agents can also cause staining without internal damage. Exposure to harsh chemicals, industrial dyes, or dark pigments in nail polish can temporarily stain the nail plate yellow or green. A specific green discoloration, known as chloronychia, is caused by the bacterial infection Pseudomonas aeruginosa, which produces a greenish-blue pigment.
Systemic Illnesses and Medication Effects
A change in toenail color can signal an underlying systemic illness or the effect of certain medications. White or pale nails, known as Terry’s nails, are characterized by a mostly opaque, ground-glass white appearance with a narrow pink or brown band at the tip. This pattern is commonly associated with chronic conditions like liver cirrhosis, congestive heart failure, or kidney failure. The change is thought to be due to decreased vascularity and an increase in connective tissue in the nail bed.
Yellow Nail Syndrome is a rare condition where nails appear yellow, thickened, and grow very slowly. This syndrome is often linked to internal issues, most notably respiratory problems such as chronic sinusitis or bronchiectasis, and lymphedema (swelling caused by lymphatic fluid buildup). Blue or gray discoloration can signal exposure to heavy metals or be a side effect of certain prescription drugs. For instance, some chemotherapy agents or the antibiotic Minocycline can cause a blue-gray tint due to pigment or drug deposition in the nail bed.
When to Seek Medical Guidance
While many instances of toenail discoloration are benign, some changes warrant medical evaluation. Consult a doctor if the discoloration is accompanied by pain, swelling, or discharge around the nail. A rapid, unexplained change in color, particularly a black streak without any history of trauma, should be checked immediately. Since only a medical professional can accurately differentiate between a fungal infection, a bruise, or a serious systemic condition, diagnosis is important if the discoloration is persistent or worsening.