A subungual hematoma is a common yet often painful condition in which blood collects beneath a fingernail or toenail after injury. Even though the nail plate appears solid and protective, the nail bed underneath is richly supplied with blood vessels and nerves. When the fingertip or toe experiences sudden trauma — such as being hit by a heavy object, smashed in a door, struck by sports equipment or repeatedly impacted during running — tiny blood vessels rupture. The trapped blood has nowhere to escape and begins to accumulate under the rigid nail plate, producing a buildup of pressure that often causes throbbing pain and dramatic discoloration.
In the early stages, the nail typically turns bright red, purple or blue-black as blood rapidly spreads under the translucent nail plate. The discoloration typically begins at the point of impact and then spreads outward. The trapped blood forms a space known as a hematoma, and because the nail cannot stretch, pressure increases quickly. This is why even small hematomas can be more painful than expected — the pain comes from pressure pushing upward on the sensitive nail bed.
Subungual hematomas are most often caused by crush injuries, such as slamming a finger in a door, dropping an object on a toe, or hitting the nail with a hammer. Athletes frequently experience this form of injury during activities like running downhill, playing soccer, basketball or martial arts, where repeated toe impact inside shoes generates microtrauma. Long-distance runners, hikers and military personnel sometimes refer to this condition as "runner’s toe" or "black toenail." Fingernail hematomas can also occur during home improvement projects, heavy labor, gym workouts and everyday accidents.
Symptoms are usually quite noticeable. The nail darkens quickly, and pain increases as pressure builds. Some people also experience swelling in the fingertip or toe, heat around the nail and tenderness when touching the affected area. In more severe cases, the nail may loosen from the nail bed or eventually fall off as healing progresses. Not all subungual hematomas require medical treatment, but understanding the severity and pain level helps determine whether intervention is needed.
If the hematoma is small and pain is mild, it will usually heal on its own. The trapped blood gradually reabsorbs, and the discoloration moves toward the nail tip over weeks as the nail grows. However, when pressure becomes intense, medical drainage — known as nail trephination — provides relief. Trephination is a simple procedure performed by a trained professional in which a small opening is created in the nail plate to allow the blood to escape. As soon as pressure is released, the throbbing pain usually decreases dramatically. Importantly, this must be done safely using sterile tools to avoid infection. Home attempts using heated objects or needles can damage the nail bed, introduce bacteria and lead to complications.
Treatment decisions depend not only on pain but also on whether there is nail bed damage or a deep cut beneath the nail. If the injury includes an open wound, the nail may need to be lifted so the underlying laceration can be stitched. In such cases, antibiotics may be prescribed to reduce the risk of infection. Severe injuries — such as crushing of the fingertip bones (distal phalanx fracture) — may require X-rays to assess structural damage. Children and adults who take blood-thinning medications can develop larger hematomas with smaller injuries and may require specialized care.
Aftercare is an important part of recovery. For the first 24 to 48 hours following the injury, elevation of the hand or foot, icing and rest help reduce swelling. If trephination has been performed, the drainage site should be kept clean and covered until fully sealed. If the nail becomes loose, it should not be forcibly removed; allowing it to detach naturally prevents unnecessary trauma to the nail bed. Toenail hematomas can be aggravated by tight footwear, so cushioned shoes and trimmed nails reduce repeated impact during recovery. Most hematomas heal without long-term consequences, although the damaged portion of the nail may take months to grow out completely. Fingernails typically take around four to six months to fully replace; toenails often require nine months or longer.
One of the most common questions from patients is whether the nail will fall off. The answer depends on how severely the nail bed was disrupted. A mild hematoma rarely causes nail loss, but a more forceful injury can detach the nail partially or completely. Even if a nail does fall off, the nail matrix — the tissue responsible for generating new nail — usually remains intact. In that case, the nail will grow back, although temporary ridges or texture changes are common during regrowth.
Prevention is much easier than treatment. Protective gloves can reduce the risk of finger injuries during mechanical work, home repairs or sports involving bats, rackets or tools. For toenails, well-fitting footwear with adequate toe space is especially important for runners and hikers. High-impact sports may require enhanced toe protection or reinforced shoes. Keeping toenails trimmed short helps reduce pressure inside shoes, while breathable socks help minimize friction and nail stress from repeated impact.
Although subungual hematomas are often minor injuries, recognizing when to seek treatment is essential. Severe pain that interferes with daily activities, bleeding under more than 50 percent of the nail area, detachment of the nail, numbness, fever or signs of infection (warmth, swelling, redness, pus) all warrant medical attention. For adults with diabetes or peripheral vascular disease, even small foot or toe injuries should be evaluated promptly to prevent complications.
Ultimately, a subungual hematoma is a visible reminder of the nail's role as a protector of the delicate tissues beneath it. When trauma strikes, the nail absorbs the blow, shielding the fingertip or toe but trapping blood in the process. Most hematomas resolve with time, while professional drainage can provide rapid relief when pain becomes severe. With proper care and patience, the nail and nail bed typically recover fully, allowing healthy new nail growth to gradually replace the damaged area.
