A crushed finger that quickly turns dark usually indicates a subungual hematoma—a bruise under the nail plate. This occurs when trauma, such as a dropped object or a slammed door, breaks the small blood vessels beneath the nail, causing blood to pool between the nail and the nail bed. The trapped blood creates pressure, causing throbbing pain and discoloration. Most of these injuries are minor and can be managed effectively with immediate at-home care.
Immediate Care for Pain and Swelling
The first step after a nail injury is to reduce swelling and throbbing pain. Immediately remove any rings or jewelry from the injured finger, as swelling can quickly make removal difficult. Apply a cold compress or ice pack wrapped in a thin cloth for 15 to 20 minutes every few hours. Cold application helps constrict blood vessels, slowing internal bleeding and reducing swelling and pain.
Elevating the injured hand above heart level uses gravity to slow blood flow, minimizing painful throbbing. Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or naproxen can manage pain and reduce swelling. Keep the area clean to prevent infection; if the skin is broken, use a loose, clean bandage for protection.
Recognizing When to Seek Medical Attention
While many subungual hematomas resolve on their own, certain symptoms warrant professional medical evaluation. Seek care if the pain is severe, unrelenting, or cannot be managed by over-the-counter medication. If the dark discoloration covers 50% or more of the nail surface, seek care, as this increases the likelihood of an associated fracture or severe nail bed laceration.
A medical provider needs to examine the digit if you notice signs of infection, such as increased warmth, swelling, pus draining, or red streaks extending from the wound. For large or severely painful hematomas, the doctor may perform trephination. This procedure uses a sterile tool to create a tiny hole in the nail plate, allowing the trapped blood to drain and immediately relieving pressure and throbbing.
The Healing and Nail Regrowth Timeline
After the initial injury or successful drainage, the discolored blood remains trapped under the nail, clotting and turning from red-purple to dark brown or black. This dark area slowly moves forward as the nail plate grows. The damaged nail will eventually detach or be pushed off entirely by the new, healthy nail growing beneath it.
The full regrowth cycle for a fingernail takes between four and six months. Fingernails grow at a rate of approximately one-tenth of an inch per month. If the damaged nail detaches completely, protect the newly exposed, sensitive nail bed by keeping it clean and covered with a bandage until the new nail offers protection. If the underlying tissue (the matrix) was severely damaged, the new nail may temporarily have an abnormal shape or texture, but it often grows back normally.