Fingernails are hard structures composed primarily of keratin, a protein also found in hair and skin. The visible, hard part is called the nail plate, which rests upon the nail bed, the soft tissue beneath it. The nail plate is nourished by the blood supply of the underlying bed. Changes in nail color, texture, or growth patterns can signal underlying health issues.
The Standard Healthy Appearance
A healthy fingernail is characterized by a pale pink coloration across the majority of the nail bed. This hue results from the dense network of capillaries visible through the translucent nail plate. The surface should be smooth and uniform, generally free of pitting or prominent horizontal grooves.
Near the base of the nail, a small, white half-moon shape called the lunula is often visible, which represents the growing edge of the nail matrix. As the nail plate grows out past the fingertip, the section no longer attached to the nail bed appears opaque white. Harmless vertical ridges running from the cuticle to the tip are common and tend to become more noticeable with age.
Colors Indicating Internal Medical Conditions
Discolorations that affect the entire nail can be a sign of systemic health problems involving major organ systems. A bluish or purplish tint, known as cyanosis, suggests that the body is not receiving adequate oxygenated blood. This change indicates a possible issue with the circulatory or respiratory system, such as certain heart conditions or chronic lung diseases like emphysema.
A generalized paleness or white appearance, excluding the free edge, can point toward anemia due to a low red blood cell count. Specific patterns of whiteness, such as Terry’s nails, are associated with severe liver disease, heart failure, or kidney failure; in this condition, the nail plate is mostly opaque white with a narrow pink or dark band near the tip. If the nails develop a widespread yellow appearance that is thick and grows slowly, it might be a rare condition called yellow nail syndrome. This syndrome is often linked to chronic respiratory disease or lymphedema, suggesting a failure in the body’s lymphatic drainage.
Small, thin red or brownish-red lines beneath the nail plate are referred to as splinter hemorrhages. While sometimes caused by minor trauma, multiple occurrences not linked to injury can signal infections of the heart valves, known as endocarditis, or vasculitis, which is inflammation of the blood vessels.
Localized Causes of Discoloration
Not all changes in nail color point to systemic illness, as many are localized to the nail unit itself or are caused by external factors. A dark brown or black discoloration is most frequently caused by trauma to the fingertip, which creates a subungual hematoma, or blood clot, beneath the nail plate. While much less common, a dark vertical band that appears suddenly or changes in appearance should be evaluated immediately, as it may be a sign of subungual melanoma, a serious form of skin cancer.
A green or blue-green color is typically caused by an infection with the bacterium Pseudomonas aeruginosa, which thrives in moist environments. This specific discoloration, often called “green nail syndrome,” is localized to the nail plate and the area between the plate and the bed. Fungal infections, or onychomycosis, frequently cause the nail to turn yellow, white, or brown, often accompanied by thickening and crumbling of the nail plate.
White spots or lines on the nail are often the result of minor, unnoticed trauma to the nail matrix. The spots grow out with the nail over time and rarely indicate a nutritional deficiency. External staining from substances like nicotine, hair dyes, or certain topical medications can also temporarily alter the nail’s color.