A blood blister under your nail, called a subungual hematoma, happens when trauma traps blood between the nail and the nail bed. The throbbing pressure can be intense, and draining it brings near-immediate relief. However, this is a procedure best performed by a healthcare provider, not at home. Attempting it yourself risks infection or further damage to the nail bed, which can permanently affect how your nail grows back.
Why It Hurts So Much
When blood pools beneath your nail after a crush injury or direct blow, it has nowhere to go. The nail plate is rigid, so the blood pushes against the sensitive nail bed underneath, creating intense, throbbing pressure. The worse the bleeding, the more pressure builds. That’s why a small bruise under the nail might just be annoying, while a large one can feel genuinely unbearable.
If the hematoma covers less than about 50% of the nail surface and you’re not in severe pain, conservative management is reasonable. That means icing it, keeping it elevated, and taking over-the-counter pain relief while letting it heal on its own. The discoloration will gradually grow out with the nail. But if the pain is significant or worsening, drainage (called trephination) is the standard treatment.
What Happens When a Doctor Drains It
Trephination is a quick, straightforward procedure that works best within 48 hours of the injury. A provider cleans the nail and surrounding skin, then uses a heated needle tip, a specialized tool, or an electrocautery device to melt or press a small hole through the nail plate directly over the center of the blood collection. The device only penetrates the hard nail itself, not the soft tissue underneath. Once the hole is made, trapped blood drains out, and the pressure drops almost immediately.
The relief is dramatic. Most people feel significantly better within seconds of the blood escaping. The procedure itself is quick enough that local anesthesia often isn’t needed, though your provider may offer it depending on how tender the area is.
Why You Shouldn’t Do This at Home
You’ll find plenty of advice online about heating a paperclip and pushing it through the nail yourself. The problem is that you can’t control how deep the tool goes. Push too far and you puncture the nail bed, turning a simple pressure problem into an open wound with a high infection risk. You also can’t properly sterilize a paperclip or sewing needle the way a medical setting can sterilize instruments.
There’s another issue: you don’t know what’s underneath. A hard blow strong enough to cause bleeding under the nail can also fracture the fingertip bone or tear the nail bed. These injuries look identical to a simple hematoma from the outside. If there’s a fracture or a deep laceration beneath the nail, poking a hole through it introduces bacteria directly into damaged tissue or even bone. A provider can assess whether you need an X-ray before deciding on treatment.
When the Injury Needs More Than Drainage
Most subungual hematomas are uncomplicated and do well with simple trephination or no treatment at all. But certain signs suggest something more serious is going on:
- Intense or worsening pain that doesn’t respond to elevation and over-the-counter pain medication
- A deep cut at or near the nail, or bleeding that won’t stop
- A misshapen or displaced nail that’s been partially lifted from the nail fold
- Suspected fracture, especially if the fingertip looks swollen, crooked, or you can’t bend it normally
When the nail has been partially torn away, when there’s a displaced fracture of the fingertip bone, or when the base of the nail (where growth starts) is disrupted, the treatment shifts from simple drainage to surgical repair of the nail bed. These cases typically need a hand surgeon or an emergency physician comfortable with nail bed reconstruction.
Signs of Infection to Watch For
Whether your hematoma was drained or you’re letting it heal on its own, keep an eye out for infection. Redness spreading beyond the immediate injury site is a warning sign, especially red streaks traveling up the finger or toe. Other signs include pus or cloudy fluid draining from under the nail, increasing swelling or pain days after the initial injury, a sensation of heat or throbbing that gets worse rather than better, and fever. Any of these warrant prompt medical attention.
How Long Recovery Takes
After drainage, the pain typically resolves quickly, but the nail itself will look discolored until it grows out completely. For fingernails, expect full regrowth in about 4 to 5 months. Toenails take considerably longer, often 10 to 18 months. During this time the nail may look dark, ridged, or slightly irregular.
In some cases, the damaged nail will loosen and eventually fall off on its own as a new nail grows in beneath it. This looks alarming but is normal. The new nail pushes the old one forward and upward until it detaches. If the nail bed wasn’t severely damaged, the replacement nail usually grows back looking normal. Significant nail bed injuries, especially ones that weren’t properly repaired, can lead to a permanently ridged, split, or misshapen nail.
What You Can Do Right Now
If you just smashed your finger and blood is pooling under the nail, start with ice wrapped in a cloth and hold your hand above heart level. This slows the bleeding and reduces swelling. Over-the-counter anti-inflammatory pain relievers can help with both the pain and inflammation. If the pain is manageable and the dark area covers a small portion of the nail, you can likely ride it out without any procedure at all.
If the pressure is severe, the hematoma is large, or the pain isn’t improving, get to an urgent care clinic or emergency room within 48 hours. Trephination is a quick visit, often takes just minutes, and the relief is immediate. Trying to tough it out for days when the pain is significant just risks the blood clotting under the nail, which makes it harder to drain later.