The nail bed is the soft tissue directly beneath the nail plate. Nail color often reflects underlying health, and redness in this area is a common concern. The cause can range from a minor injury to an indicator of a chronic systemic illness. Understanding the source requires recognizing the anatomy of the nail unit and the pattern of the redness.
The Vascular Mechanism of Nail Bed Color
The naturally pink or reddish tone of the nail bed results from its abundant blood supply. This tissue is richly perfused with a dense network of small blood vessels and capillary loops, visible through the transparent nail plate. The color is essentially the red of oxygenated blood circulating beneath the surface.
Redness develops when the volume of blood increases, either through vasodilation (widening of the blood vessels) or localized hemorrhage (bleeding). Vasodilation, often a response to heat or inflammation, causes a temporary flush of color. A distinct red mark, conversely, usually indicates blood that has leaked out of the vessels and is trapped beneath the nail plate.
Common Localized Causes of Redness
The most frequent cause of localized redness is direct physical trauma, resulting in a subungual hematoma. This occurs when a crush injury, such as slamming a finger in a door, ruptures the underlying blood vessels. The pooling of blood between the nail plate and the nail bed initially appears red or purplish, darkening to brown or black as it clots.
A larger collection of blood creates significant throbbing pain due to pressure under the nail. Another non-infectious cause is chronic, repetitive microtrauma, such as from aggressive manicuring or tools that apply constant pressure. This repeated irritation can cause inflammation and persistent, mild redness.
Redness can also arise from irritant contact dermatitis, a non-allergic inflammatory reaction. Frequent exposure to harsh chemicals, detergents, or solvents can break down the skin barrier around the nail folds, causing generalized redness. Acute allergic reactions to nail products, such as certain adhesives or components in gel polishes, can similarly trigger localized redness and inflammation.
Redness Due to Infection and Acute Inflammation
Infection presents distinct symptoms that differentiate it from simple trauma or irritation. The most common infectious cause of redness is paronychia, an infection of the skin surrounding the nail fold. This condition often begins when the skin is broken by injury, nail-biting, or aggressive cuticle trimming, allowing bacteria or fungi to enter.
Acute paronychia is typically bacterial and develops rapidly, presenting with intense redness, swelling, warmth, and throbbing pain around the edge of the nail. Often, a visible collection of pus, or an abscess, forms beneath the skin of the nail fold. Chronic paronychia, lasting six weeks or more, is often caused by fungus and results in less acute redness but persistent swelling and tenderness.
If the infection spreads deeper into the fingertip tissue, it is known as cellulitis. This spreading infection causes the area of redness to expand and can be accompanied by systemic symptoms like fever. Expanding, warm, painful redness and the presence of pus are clear signs that a biological invasion is the root cause of the discoloration.
Pattern-Based and Systemic Indicators
Certain patterns of redness can indicate internal or widespread health issues. One such pattern is a splinter hemorrhage, which appears as small, thin, red or reddish-brown lines running vertically with nail growth. These lines are caused by minor damage to the capillaries, resulting in tiny blood clots or leaked blood.
Trauma is the most common cause, especially if only one nail is affected. However, their presence in multiple nails without injury can be significant. They are a classic finding in bacterial endocarditis, an infection of the heart’s inner lining, where small emboli travel to the nail bed vessels.
Splinter hemorrhages may also be associated with systemic conditions that cause inflammation of the blood vessels.
Conditions Associated with Splinter Hemorrhages
Another significant pattern is the red lunula, where the half-moon shape at the base of the nail, normally white, appears distinctly reddish. This finding is rare and is linked to various systemic diseases. The red lunula is thought to be caused by increased blood flow or vasodilation in the underlying vascular network, making the blood color more visible.
Conditions Associated with Red Lunula
Knowing When Medical Evaluation Is Necessary
While many instances of localized redness resolve naturally, a medical evaluation is warranted under certain circumstances. If the redness is persistent, does not improve within a few days, or appears without a clear history of trauma, it should be assessed by a healthcare provider. Non-traumatic redness that accompanies changes in the nail’s shape or texture also requires professional attention.
Immediate evaluation is necessary if the redness is accompanied by signs of a spreading infection, such as a fever or red streaks extending away from the nail. Severe or throbbing pain, especially with a large subungual hematoma, may require drainage to relieve pressure. The appearance of splinter hemorrhages in multiple nails without a known injury warrants a prompt medical work-up to rule out serious systemic conditions.