Slamming your finger in a car door often results in intense pain and a dramatic change in nail color. This trauma causes a subungual hematoma, which is the pooling of blood underneath the hard nail plate. The initial shock gives way to a deep, throbbing ache, signaling significant damage to the delicate tissues beneath the nail. Understanding the injury and knowing how to manage it immediately is the first step toward recovery.
Immediate Care and Pain Management
The moments immediately following the injury are crucial for reducing swelling and managing pain. First, remove any rings from the injured finger, as rapid swelling can quickly cut off circulation. If the skin around the nail is broken, gently clean the area with mild soap and water.
To minimize inflammation, apply a cold compress, such as ice wrapped in a thin towel, for 10 to 20 minutes at a time. This helps restrict blood flow to the injured site, reducing both swelling and pain. Elevate the injured hand above the level of your heart to slow blood flow, which decreases the internal pressure causing the throbbing sensation. Over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or naproxen can decrease inflammation and manage discomfort.
What Causes the Black Nail Discoloration
The striking black or deep purple color under your nail is the direct result of crush trauma rupturing small blood vessels in the nail bed. The nail bed is sensitive tissue beneath the nail plate containing a dense network of capillaries. When the finger is crushed, blood vessels tear, releasing blood into the confined space between the nail plate and the nail bed.
Because the rigid nail plate is firmly attached to the nail bed and cannot expand, the pooling blood becomes trapped, forming the subungual hematoma. This accumulation quickly clots and oxidizes, causing the distinctive dark coloration. The severe, throbbing pain results from the increasing pressure created by the pooled blood pushing against the sensitive nerve endings in the nail bed.
Signs That Require Professional Medical Attention
While many subungual hematomas can be managed at home, certain signs indicate the need for professional medical evaluation to prevent complications.
When to Seek Medical Attention
Seek attention if the pain is severe and unremitting, meaning it is not relieved by elevation or over-the-counter medication, as this suggests dangerously high pressure beneath the nail. A hematoma covering more than 50% of the nail surface also increases the likelihood of an underlying injury to the nail bed or bone.
It is important to look for signs of a potential fracture, such as an inability to move the finger, a visibly crooked or deformed appearance, or significant swelling that extends beyond the injury site. In such cases, an X-ray may be needed to check for a fracture of the distal phalanx, the fingertip bone.
If you notice signs of infection—which may develop a few days later—like increasing redness, warmth, pus draining from the wound, or a fever, you should see a healthcare provider promptly. For painful, large hematomas, a medical professional may perform a procedure called trephination.
This involves carefully drilling a small hole through the nail plate to release the trapped, clotted blood, instantly relieving the pressure and the intense throbbing pain. This procedure must only be performed by a professional, as attempting to drain the blood yourself risks introducing bacteria and causing a serious infection.
Long-Term Healing and Nail Replacement
Once the initial trauma has passed, the body begins the long process of healing and replacing the damaged nail. The pooled blood under the nail remains trapped, and the discoloration gradually migrates outward as the new, healthy nail grows from the matrix at the base. Eventually, the damaged nail plate will separate from the nail bed due to the pressure from the hematoma and the growth of the new nail underneath, causing the old nail to lift and fall off.
The complete regrowth of a fingernail is a slow process, typically taking between four and six months for the new nail to fully replace the old one. While the old nail lifts or after it has fallen off, the exposed nail bed is sensitive and vulnerable to injury and infection. Keep the exposed area clean and protected with a non-stick bandage until the new nail has grown out enough to shield the tissue beneath it. Protecting the nail matrix is essential to ensure the new nail grows back normally.