Nails often reflect overall health, and their appearance can signal various underlying conditions. Healthy nails typically present as smooth surfaces with a uniform, pinkish color, free from deep ridges or spots. When nails turn brown, it can indicate a range of issues from simple external factors to more complex internal health concerns.
External Stains and Trauma
Brown discoloration on nails sometimes results from external contact or physical injury. Substances like nicotine and tar from cigarettes can cause yellowish-brown stains on both the nails and surrounding skin. Similarly, hair dyes, certain chemicals, or even some nail polishes can stain nails upon contact. These can lead to temporary discoloration.
Physical trauma, such as stubbing a toe or hitting a finger, can cause a subungual hematoma, a collection of blood under the nail. This trapped blood may initially appear red or purple, then evolve to dark brown or black as it clots. This discoloration typically grows out with the nail over several months, as the nail plate regenerates.
Infections
Infections are another common cause of brown nail discoloration. Fungal infections (onychomycosis) frequently affect nails, causing them to change color, often to yellow, brown, or black. These infections typically begin at the tip or sides of the nail, spreading towards the cuticle and leading to thickening, brittleness, or crumbling. The fungi involved feed on keratin, the primary protein composing the nail, leading to these structural changes.
While fungal infections are a primary cause for brown nails, bacterial infections can also play a role. Pseudomonas aeruginosa can cause a greenish-black or brownish discoloration, known as chloronychia or green nail syndrome. This bacterium thrives in moist environments, often affecting individuals whose hands or feet are frequently wet. The green pigment is due to compounds produced by the bacteria.
Internal Health Indicators
Nail discoloration can signal underlying systemic health conditions or medication side effects. Chronic diseases, including kidney disease, liver disease, thyroid disorders, and diabetes, can manifest changes in nail appearance. Autoimmune conditions like lupus and rheumatoid arthritis, along with certain lung diseases or HIV infection, have also been associated with nail abnormalities. These changes occur because systemic conditions affect the overall health and growth of the nail matrix.
Certain medications can induce nail discoloration. Chemotherapy drugs are known for causing various nail changes, including brown or black pigmentation. Some antibiotics (e.g., tetracyclines, minocycline) and antimalarial drugs can also lead to discoloration. Other medications, including lithium and some anti-seizure drugs, have been linked to changes in nail color or texture.
A rare but significant cause of brown or black nail discoloration is subungual melanoma, a serious form of skin cancer under the nail. It often appears as a dark, vertical streak that may widen or change over time, affecting any nail, though more common on the thumb or big toe. Unlike a bruise, which grows out, a melanomatous streak typically persists and may show irregular borders or extend to the skin around the nail (Hutchinson sign).
When to Seek Medical Advice
Given the varied causes, seek medical evaluation for persistent or concerning changes. Consult a healthcare professional if discoloration does not resolve on its own, especially if it appears without known trauma. Signs warranting medical attention include pain, swelling, or redness around the nail.
Other indicators for a medical visit include changes in the nail’s shape or texture, such as thickening, brittleness, or separation from the nail bed. A rapidly progressing discoloration or a dark streak that widens, changes intensity, or extends to the cuticle should prompt immediate professional assessment. Early diagnosis is important, particularly when ruling out more serious underlying conditions.