Fingernails and toenails are complex structures composed of keratin that often serve as visible indicators of internal health. The nail plate is translucent, meaning the color observed is primarily the result of blood flow in the underlying nail bed. Changes in the nail’s appearance, whether in color, texture, or shape, can signal localized issues like infection or trauma, or point toward systemic diseases. Monitoring these subtle shifts offers important clues about overall well-being.
The Appearance of Healthy Nails
A healthy nail typically presents a uniform pink color across the nail bed due to the rich supply of blood vessels beneath it. The portion of the nail that extends past the finger, known as the free edge, appears white because it no longer rests on the vascular nail bed. At the base, the lunula, or “half-moon,” is a normal variation of the nail matrix that appears white because the cells are still immature. The nail surface should be smooth, without significant ridges, pitting, or discoloration.
White and Pale Nail Indications
Excessive whiteness or paleness across the nail plate, known as leukonychia, often signals an issue affecting the nail bed rather than the nail plate itself. One specific pattern is Terry’s nails, where the nail is mostly white with a narrow pink or brownish band at the tip. This pattern suggests potential issues with the liver, kidneys, or heart failure. The white color is caused by changes in the nail bed’s connective tissue, which reduces the visibility of underlying blood vessels.
Overall paleness of the nail bed, without the specific pattern of Terry’s nails, can indicate anemia, a condition characterized by a low red blood cell count. White spots or lines, often called punctate leukonychia, are common and usually result from minor trauma to the nail matrix. These spots are typically harmless and will simply grow out with the nail.
Yellow and Green Nail Indications
A yellow discoloration is a frequent sign of a fungal infection, known as onychomycosis, which can also cause the nail to thicken and crumble. This yellowing is a localized issue, often treatable with antifungal medications. In rare instances, persistent yellowing accompanied by slow-growing, thickened nails and swelling in the legs (lymphedema) may indicate Yellow Nail Syndrome, a condition associated with respiratory problems.
Non-medical causes, such as smoking or the prolonged use of dark-colored nail polishes without a base coat, can also stain the nail plate yellow. A distinct green or greenish-black color, called chloronychia or green nail syndrome, is usually caused by the bacterium Pseudomonas aeruginosa. This bacterium thrives in moist environments, often colonizing the space under a separated nail, producing characteristic blue-green pigments.
Dark and Blue Nail Indications
Dark colors—ranging from red and purple to black and brown—are commonly the result of trauma, known as a subungual hematoma. This is a bruise under the nail caused by blood pooling between the nail plate and the nail bed, which gradually resolves as the nail grows out.
A more concerning dark presentation is a pigmented band running vertically from the base to the tip, called melanonychia, caused by an activation of pigment-producing cells. While most cases are benign, a dark streak that is new, widening, or shows irregular borders may signal subungual melanoma, a serious form of skin cancer. Clinicians use criteria like the ABCDEF rule to assess these streaks, looking for features such as a wide, brown-black band and the extension of pigment onto the surrounding skin (Hutchinson sign).
Blue or grayish nails are often a signal of cyanosis, which indicates a lack of sufficient oxygen circulating in the blood. This condition is sometimes linked to heart or lung issues.
When Nail Color Changes Require a Doctor Visit
A consultation with a healthcare provider is prudent for any nail discoloration that persists, is unexplained, or is accompanied by other symptoms. Professional evaluation is necessary if a dark streak under the nail is new, rapidly changing, or has pigment bleeding onto the surrounding skin. Any blue discoloration of the nail beds, especially coinciding with breathing difficulties, warrants immediate medical attention as it indicates low blood oxygen levels. Persistent yellowing that causes the nail to thicken and detach, or any color change accompanied by swelling, pain, or pus, suggests an infection or underlying condition requiring treatment.