That dark, throbbing discoloration under your nail is almost certainly a subungual hematoma, which is a pocket of blood trapped between the nail plate and the nail bed after a blow or crush injury. In most cases it looks worse than it is, and mild ones heal on their own as the nail grows out. But the size of the bruise, the level of pain, and a few other details determine whether you can manage this at home or need a doctor to intervene.
What Is Actually Happening Under the Nail
The nail bed sits directly on top of the bone at the tip of your finger, and it is packed with tiny blood vessels. When something smashes the fingertip, those vessels rupture and blood pools in the tight space between the nail bed and the hard nail plate above. Because the nail plate does not flex much, the blood has nowhere to go. It sits there, clots, and turns dark red, purple, or black depending on how much has accumulated and how long it has been there.
The throbbing pain you feel comes directly from pressure. Blood keeps pooling, the space cannot expand, and the nerve endings in the nail bed get compressed. This is why the first few hours after the injury tend to be the worst. Once the bleeding stops and pressure stabilizes, the pain usually starts to ease on its own, though it can remain tender for days.
What You Should Do Right Away
In the first minutes after the injury, a few simple steps help limit swelling and pain:
- Ice: Wrap ice or a cold pack in a cloth and hold it against the finger for 15 to 20 minutes at a time, with breaks in between. Cold narrows blood vessels and slows the accumulation of blood under the nail.
- Elevation: Keep your hand raised above heart level. This sounds overly simple, but gravity genuinely reduces the amount of blood flowing into the injured fingertip.
- Compression: A gentle wrap around the finger can limit swelling, though avoid wrapping so tightly that circulation is cut off. If the fingertip turns white or numb, loosen it immediately.
- Pain relief: Over-the-counter anti-inflammatories like ibuprofen help with both pain and swelling. Acetaminophen works for pain alone if anti-inflammatories are not an option for you.
These measures are enough for a small hematoma, one that covers less than roughly a quarter of the nail and causes only moderate discomfort. If the pain is manageable after the first day and the finger moves normally, you are probably fine watching and waiting.
When You Need to See a Doctor
A few signs push this from a wait-and-watch situation to one that needs medical attention:
- The dark area covers half the nail or more. A large hematoma suggests more extensive bleeding and increases the chance that the nail bed underneath has been torn or lacerated.
- The pain is severe and not improving. Intense, unrelenting throbbing usually means the pressure under the nail is high enough that it will not resolve without drainage.
- The nail is lifted, cracked, or partially detached. If the nail itself is damaged rather than just discolored, the nail bed below may be lacerated and could need repair to avoid permanent deformity.
- The finger is misshapen, extremely swollen, or you cannot bend it. These suggest a possible fracture of the bone at the tip of the finger, called the distal phalanx.
- The skin around the nail is broken and dirty. Open wounds combined with crush injuries carry a higher infection risk and may need cleaning, antibiotics, or a tetanus booster.
You do not need to rush to an emergency room for every black nail, but if any of those signs are present, getting seen within a day or two matters. Delayed treatment of a lacerated nail bed is harder to repair and more likely to leave a lasting problem.
How a Doctor Drains the Blood
The standard treatment for a painful subungual hematoma is a procedure called trephination, which means making a small hole through the nail plate to let the trapped blood escape. It sounds alarming, but the nail plate itself has no nerve endings, so the drilling or melting through it is painless. You feel dull pressure rather than sharp pain during the process.
A heated paperclip, a needle, or a small electrocautery device is used to burn or bore through the nail plate until it reaches the blood pocket. Once the hole is through, dark blood drains out immediately and the pressure drops. Patients typically experience substantial relief in pain over the hours following the procedure.1PubMed. Controlled nail trephination for subungual hematoma The small hole that is created decreases the internal pressure under the nail and allows the blood to keep draining as needed.2PubMed Central. Subungual Hematoma Drainage Following Foot Trauma
After trephination, you keep the finger clean and bandaged. The hole in the nail eventually grows out with the rest of the nail plate over the following months. The procedure itself takes only a few minutes and is done in an emergency department or urgent care setting, usually without any anesthesia beyond a cold spray in some cases.
When the Nail Bed Itself Needs Repair
Trephination works well when the nail bed underneath is intact and the only problem is trapped blood. But if the nail bed has been torn, which is more likely with larger hematomas or crush injuries where the nail is cracked or lifted, the treatment becomes more involved. In these cases the nail plate needs to be removed so the doctor can see and repair the underlying tissue.
Nail bed lacerations are sutured under magnification because the tissue is delicate and precise alignment matters for how the new nail will grow.3PubMed Central. Surgical treatment of acute fingernail injuries If the matrix, the crescent-shaped tissue at the base of the nail where new nail cells are produced, is damaged and not repaired carefully, the nail that eventually regrows can be ridged, split, or permanently deformed.4PubMed Central. Nail bed injuries and deformities of nail This is one reason doctors take even seemingly minor nail injuries seriously when the nail plate itself is disrupted. What looks like just a cosmetic issue on the surface can mean a structural problem underneath that affects nail growth for years.
After a nail bed repair, the removed nail plate (or a silicone substitute) is often placed back over the nail bed to act as a splint, protecting the repair and guiding the new nail as it grows in. Full regrowth of a fingernail takes roughly three to six months, so patience is part of the recovery.
Could There Be a Broken Bone Under There
Yes, and this is one of the things people most often miss. The bone at the tip of your finger sits directly beneath the nail bed, and the same blow that causes a black nail can crack or fracture that bone. These are called tuft fractures because they affect the fan-shaped tip of the distal phalanx, and they happen frequently with direct impact or crush injuries.5Symbiosis Online Publishing. Conservative Treatment for Subungal Hematoma with Tuft Fracture
The tricky part is that a tuft fracture can feel a lot like a bad bruise: throbbing pain, swelling, tenderness. You might not suspect a break because you can still wiggle the finger. But the presence of a fracture changes how the hematoma should be managed. When more than half the nail plate is dark with blood and an X-ray reveals a fracture underneath, guidelines generally call for removing the nail, draining the blood, and inspecting the nail bed for lacerations that need repair.5Symbiosis Online Publishing. Conservative Treatment for Subungal Hematoma with Tuft Fracture The fracture itself usually does not need surgery. Most tuft fractures heal with a protective splint over a few weeks. But having the fracture changes what needs to happen with the soft tissue above it, which is why an X-ray is worth getting if the injury was forceful.
What to Expect as the Nail Grows Out
If the nail bed is intact and you either let a small hematoma be or had it drained, the dark discoloration gradually moves toward the tip of your finger as the nail grows. A fingernail grows at roughly three to four millimeters per month, so a hematoma near the base of the nail can take four to six months to fully grow out. During that time, the nail may look strange, with a dark streak or patch that slowly shifts forward. This is normal and cosmetic. Once the discolored portion reaches the free edge of the nail and is trimmed away, the nail behind it should look healthy.
If the nail falls off, which happens sometimes with larger hematomas or when the nail was already loosened by the injury, the nail bed underneath looks raw and tender but usually heals well if kept clean and protected. A new nail begins growing from the matrix within a few weeks, though the full replacement nail takes months to fill in completely. During the regrowth period, the exposed nail bed is sensitive, so wearing a bandage and avoiding direct pressure on the fingertip helps.
Permanent nail changes after a hematoma are uncommon when the nail bed was not torn. But if the matrix was damaged, ridges, splits, or a thickened nail can result. Proper management of the initial injury is the single best predictor of whether the nail grows back normally.4PubMed Central. Nail bed injuries and deformities of nail This is worth remembering if you are debating whether to see a doctor. Getting the nail bed assessed and repaired early prevents problems that are much harder to fix later.
When Children Slam Their Fingers
Crushed fingertips are one of the most common childhood injuries. At just one children’s hospital in Scotland, over 300 children a year were treated for crushed fingertips, and the researchers estimated that about six percent of children under age 13 suffer this type of injury at some point.6Journal of Hand Surgery. Meshed adhesive tape for the treatment of crushed fingers in children The majority happen at home, with doors being the usual culprit.
Children’s fingertips deserve extra caution for a couple of reasons. Their nail beds are still developing, and damage to the growth matrix can affect nail formation as the child grows. They are also less able to describe exactly how much pain they are in or whether the finger feels “wrong” in a way that might suggest a fracture. If a child’s fingernail turns black after being slammed in a door, a trip to the pediatrician or urgent care is a good default, especially if the child is reluctant to use the finger or the swelling is significant. Doctors can check for fractures, assess whether the nail bed needs attention, and decide whether trephination would help with pain.
Injuries You Might Not Think Of
Doors and hammers get all the attention, but subungual hematomas show up across a range of scenarios. Athletes who play sports involving repeated impact to the hands or feet, such as basketball, rock climbing, or distance running, can develop black nails from chronic microtrauma rather than a single blow. Runners in particular are familiar with black toenails caused by the toe repeatedly hitting the front of the shoe over long distances. These chronic hematomas follow the same basic pattern as acute ones but tend to be less painful because the blood accumulates gradually.
In occupational settings, hand and finger injuries are disproportionately common. A study of construction workers found that hands and fingers were the predominant body part injured in nail-gun incidents, accounting for the vast majority of cases.7Applied Occupational and Environmental Hygiene. Nail gun injuries among construction workers While nail-gun injuries are more severe than a typical door slam, the point stands that fingertips are vulnerable in any setting where tools are in use, and wearing proper gloves or using safety guards prevents many of these injuries entirely.
When a Dark Nail Is Not From an Injury
If you notice a dark streak or patch under your nail but cannot recall any injury, pause before assuming it is just a bruise you forgot about. Several conditions can darken the nail without trauma.
Subungual melanoma is a rare but serious form of skin cancer that appears as a dark band or patch under the nail. It accounts for a small fraction of melanoma cases overall, but it is disproportionately common in people with darker skin tones and is often diagnosed late because people assume it is a bruise or a fungal infection. The key difference is that a hematoma grows out with the nail over weeks and months, while a melanoma streak stays in place or widens because the pigment is being produced continuously by abnormal cells in the nail matrix. If you see a dark line under the nail that does not move with nail growth, or if the pigment starts spreading into the skin around the nail (a sign called Hutchinson’s sign), see a dermatologist promptly.
Fungal infections can also turn nails dark, typically producing a thickened, crumbly nail along with the discoloration. Green discoloration sometimes indicates a bacterial infection. And certain medications, including some chemotherapy drugs and antimalarials, can cause darkening of the nails as a side effect. The distinguishing feature of a traumatic hematoma is always the history: you hit the finger, the nail turned dark soon afterward, and the dark area moves toward the tip over weeks. If any of those pieces are missing, it is worth investigating further.
Why Fingertips Are So Sensitive to Begin With
There is a reason a smashed finger feels so disproportionately awful compared to, say, a bruise on your forearm. The fingertip is one of the most nerve-dense areas of the human body. The broad, flat pad at the end of each finger evolved specifically for fine touch and manipulation of small objects, and the nail plate above it serves as a rigid backing that enhances the sensitivity of the pad.8Journal of Human Evolution. Phylogeny of the nail That rigid plate is great for gripping and sensation, but it also means that any swelling underneath has no room to spread out. The result is an outsized pain response relative to the size of the injury, which is your body’s way of telling you to protect an area it relies on heavily.
This also explains why even a well-treated subungual hematoma can remain tender for a surprising amount of time. The nail bed and fingertip pad stay sensitive during healing, and bumping the injured finger during daily activities can reignite the soreness. Being deliberate about protecting the finger with a splint or buddy-taping it to an adjacent finger for the first week or two makes a real difference in comfort during recovery.