Red coloring under your nails usually comes from blood vessels in the nail bed showing through more than normal, trapped blood from an injury, or changes in the nail plate that let underlying color shift. Most causes are harmless, but a few patterns signal something worth investigating. The key is identifying where the redness appears, how many nails are affected, and whether it came on suddenly or gradually.
Injury and Trapped Blood
The most common reason for redness (or a dark red-to-purple patch) under a nail is a subungual hematoma, which is blood trapped between the nail plate and the nail bed after some kind of trauma. You don’t need to slam your finger in a door for this to happen. Repetitive pressure from tight shoes, running, or even drumming your fingers can cause small bleeds that show as red or bluish-black spots under the nail.
A fresh hematoma often throbs and looks deep red before darkening over the next day or two. Because the blood gets incorporated into the nail plate, it has to grow out with the nail. For fingernails, that takes roughly six months from the base to the tip. Toenails take closer to a year. If the blood pool covers a large portion of the nail surface and the pain is significant, a doctor can relieve the pressure by making a small hole in the nail plate to drain the fluid.
Splinter Hemorrhages
If the redness looks like thin, vertical red or reddish-brown lines running the length of your nail, those are splinter hemorrhages. They’re caused by tiny bleeds in the capillaries of the nail bed. Minor trauma is the most common explanation, especially if you work with your hands.
Splinter hemorrhages get more attention in medicine because they can be a sign of infective endocarditis, an infection of the heart valves. In practice, though, only about 26% of people with confirmed endocarditis actually have splinter hemorrhages, so the connection isn’t as strong as older textbooks suggested. Still, if you notice new splinter hemorrhages alongside fever, fatigue, or unexplained weight loss, it’s worth getting checked.
Red Lines Running From Base to Tip
A single red streak running the full length of one nail is called longitudinal erythronychia. When it appears on just one finger, it’s typically linked to a small benign growth in the nail matrix (the tissue under the base of your nail that produces the nail plate). In rare cases, a single red line can indicate a squamous cell carcinoma or an amelanotic melanoma under the nail, both of which lack the dark pigmentation people associate with skin cancer.
When red lines appear on multiple nails at once, the cause is more likely a systemic skin condition like lichen planus or psoriasis rather than a localized growth. Multiple-nail redness that develops gradually and doesn’t hurt is less worrisome than a single painful streak on one finger, but both patterns deserve a dermatologist’s evaluation if they persist.
Redness in the Half-Moon Area
The lunula is the pale crescent at the base of your nail. When it turns red instead of its usual white or light pink, it can reflect an underlying condition. Red lunulae have been documented in rheumatoid arthritis, lupus, alopecia areata, heart failure, liver cirrhosis, psoriasis, and even carbon monoxide poisoning. A single episode of red lunulae without other symptoms isn’t necessarily alarming, but persistent redness across multiple nails is a signal your body may be dealing with something systemic.
Half-and-Half Nails
If the bottom half of your nail looks white while the outer portion (the part closer to the tip) appears distinctly red, pink, or brown, you may be looking at a pattern called Lindsay nails. The colored band typically covers 20% to 60% of the nail length, with a sharp line separating it from the white zone. This pattern is most closely associated with chronic kidney disease, though it can also appear with liver cirrhosis, Crohn’s disease, and diabetes.
A similar but subtler version called Terry nails shows a very narrow colored band (just a few millimeters wide) at the tip, with the rest of the nail appearing white. Terry nails are linked to cirrhosis, congestive heart failure, and adult-onset diabetes. In both cases, the discoloration doesn’t fade when you press on the nail, which helps distinguish it from normal blood flow changes.
Psoriasis and the “Salmon Patch”
Nail psoriasis can produce a distinctive reddish or yellowish-brown discoloration under the nail called a salmon patch or oil drop sign. It happens when abnormal skin cell turnover in the nail bed creates a small pocket where serum and cellular debris collect. The spot usually has a brownish margin separating it from the surrounding healthy pink nail. If it extends to the edge of the nail, the nail plate may start lifting away from the bed. People who already have psoriasis on their skin develop nail involvement in up to half of cases, so the connection is strong if you have a known diagnosis.
Infections Around the Nail
Redness concentrated along the sides or base of the nail, rather than underneath it, often points to paronychia, an infection of the skin folds surrounding the nail. The area becomes swollen, warm, and tender. Acute paronychia usually follows a hangnail, nail biting, or an aggressive manicure that opens a path for bacteria. If the infection isn’t treated, it can spread under the nail plate to the other side, creating a more extensive pocket of pus. Fungal nail infections, by contrast, tend to produce white or yellowish discoloration rather than redness.
Glomus Tumors
A glomus tumor is a rare, usually benign growth that forms in the nail bed and can create a reddish or bluish-red spot visible through the nail. What makes it distinctive is a triad of symptoms: pinpoint tenderness directly over the spot, intense bursts of pain that seem wildly out of proportion to the size of the lesion, and sensitivity to cold. Something as minor as holding a cold drink or reaching into a refrigerator can trigger pain. The pain episodes are typically short, sometimes less than a minute, but can leave you needing hours to recover. These tumors are small and treatable with surgery, but they’re frequently misdiagnosed for years because they don’t always show up clearly on imaging.
When Redness Needs Evaluation
A nail that changes color, changes shape, begins lifting from the bed, develops dents or thickens noticeably, or shows a new dark or red line should be evaluated by a healthcare provider. Single-nail changes are generally more concerning than changes across all nails, because localized abnormalities can indicate a growth that may need a biopsy for definitive diagnosis. Redness across many nails at once is more likely tied to a systemic condition, medication side effect, or skin disease, all of which benefit from early identification.
If your nail redness followed an obvious injury and is growing out gradually without worsening pain, you’re most likely watching a simple hematoma resolve on its own. If it appeared without trauma, hasn’t changed in weeks, or is accompanied by pain or other symptoms, that’s the point where getting a professional look becomes worthwhile.