A dark discoloration under a nail following an injury is medically known as a subungual hematoma. This condition occurs when trauma, such as a crushing blow or a severe stubbing, ruptures small blood vessels in the sensitive nail bed beneath the nail plate. Since the blood is trapped by the rigid nail, it pools in this confined space, causing intense, throbbing pain due to the resulting pressure. The degree of pain is directly related to the volume of blood collected.
Identifying Subungual Hematoma Severity
Assessing the extent of the injury determines whether home care is appropriate or if immediate professional medical attention is required. Seek a medical evaluation if the hematoma covers more than 25% to 50% of the visible nail surface, or if severe, unrelenting throbbing pain does not subside shortly after the injury.
Signs of an underlying fracture to the bone beneath the nail, known as the distal phalanx, include a significant crush injury or difficulty moving the affected digit. An X-ray may be necessary to rule out a fracture, as this complication requires different management. Prompt medical intervention is also necessary for any sign of infection, such as increasing redness, warmth, pus draining from under the nail, or a fever.
Immediate Steps for Pain Relief and Minor Cases
For small hematomas that do not involve severe pain or signs of deeper injury, managing the symptoms is the primary focus until the body naturally reabsorbs the trapped blood. The R.I.C.E. principles offer a structured approach to initial care, starting with resting the injured digit. Applying a cold compress or ice pack, wrapped in a cloth, helps reduce swelling and dull the initial pain.
Elevating the injured hand or foot above the level of the heart minimizes blood pooling and swelling. Taking over-the-counter non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen aids in pain management and reduces inflammation. Keep the area clean and protected, as a compromised nail bed creates a potential entry point for bacteria.
Medical Drainage Procedures
For larger or acutely painful hematomas, the definitive treatment is nail trephination, performed by a healthcare professional. The goal of this procedure is to relieve the painful pressure caused by the trapped blood. The physician makes a small, controlled hole through the nail plate directly over the blood collection.
This opening allows the pooled blood to drain, often providing immediate relief from the throbbing sensation. Trephination tools are sterile and specialized, such as a needle, a small drill, or an electrocautery device that melts a precise hole through the nail. This procedure must never be attempted at home due to the significant risk of introducing infection or causing permanent damage.
The sterile environment of a medical office ensures the procedure is performed safely. After drainage, the area is typically dressed with a sterile bandage to manage residual drainage over the following day or two. While the procedure addresses the immediate pain, the dark stain from the remaining clotted blood will still be visible.
The Long-Term Healing Process
Once the immediate pressure is relieved or the small hematoma is managed at home, the focus shifts to long-term recovery, which depends entirely on nail growth. The dried blood remains fixed to the nail bed until the entire nail grows out. For fingernails, this process takes approximately six to nine months, while a toenail may require 12 to 18 months for complete replacement.
In cases where the initial trauma was severe, the accumulated blood may separate the old nail from the nail bed, causing the nail to eventually loosen and shed. A new, healthy nail will grow in to replace it, pushing the damaged nail off over several weeks or months. Severe injury to the nail matrix, the tissue responsible for nail production, can result in the new nail growing back with a temporary or permanent deformity.