When a heavy object strikes the toe, the resulting intense pressure and discoloration under the nail is a common but painful injury. This condition is medically known as a subungual hematoma, which is a collection of blood trapped beneath the nail plate. The dark, bruised appearance signals that blood vessels in the underlying tissue have been ruptured by the trauma. While often alarming, this injury is usually minor and manageable at home, but certain signs indicate the need for professional medical attention.
Understanding the Subungual Hematoma
The mechanism of a black toenail is a direct result of the toe’s anatomy and the force of the injury. When trauma crushes the end of the toe, small blood vessels in the nail bed (the soft tissue beneath the nail) tear and bleed. This bleeding forms a pool of blood, the hematoma, in the restricted space between the nail bed and the rigid nail plate.
The trapped blood coagulates, leading to the characteristic blue, purple, brown, or black appearance visible through the nail. Since the toenail is firmly attached, the pooling blood has nowhere to escape, creating significant pressure and causing the intense, throbbing pain associated with the injury.
Immediate At-Home Care
For minor injuries where pain is tolerable and discoloration covers only a small portion of the nail, immediate at-home care can manage symptoms. Following the R.I.C.E. principles—Rest, Ice, Compression, and Elevation—is the recommended first step. Rest the injured foot and apply an ice pack wrapped in a cloth to the toe for 15 to 20 minutes at a time to reduce swelling and dull the pain.
Gentle compression, such as a loose wrap, helps prevent additional pooling of blood. Elevating the foot above the level of the heart for the first few days aids in reducing swelling. Over-the-counter pain relievers, like acetaminophen or ibuprofen, can manage discomfort and inflammation.
Identifying When Professional Medical Attention is Needed
While many subungual hematomas resolve on their own, certain signs indicate the need for professional medical evaluation.
Extent of Discoloration
If the black or purple area covers 50% or more of the nail surface, seek care. This large size suggests a higher probability of an underlying nail bed laceration that may require surgical repair.
Severe Pain
Severe, unrelenting, or throbbing pain not relieved by ice and elevation signals excessive pressure from the trapped blood. A medical professional can perform trephination, which involves making a tiny hole in the nail plate to drain the blood and immediately relieve the pressure. This procedure should never be attempted at home due to the high risk of infection.
Potential Fracture or Infection
A serious crush injury carries the risk of a distal phalanx fracture (a break in the bone at the tip of the toe). If you have difficulty bearing weight, notice deformity, or experience pain when moving the toe, an X-ray may be necessary. Signs of infection also require immediate medical attention. These include increasing redness, swelling, warmth, pus draining from the area, or red streaks extending from the toe.
The Long-Term Healing and Nail Regrowth Process
The black discoloration is not permanent but will slowly move outward as the toenail grows. Since toenails grow slowly (typically 1.5 to 2 millimeters per month), it takes a significant amount of time for the black area to reach the tip and be trimmed away. Full regrowth after a severe injury can take 12 to 18 months.
The pressure from the hematoma often causes the nail plate to separate from the nail bed, a process known as onycholysis. This separation may result in the entire old nail eventually lifting and detaching, which is a normal part of healing. If the damaged nail comes off, protect the newly exposed, sensitive nail bed with a clean, non-stick bandage until the new, healthy nail grows out. If the trauma damaged the nail matrix (the area responsible for producing new cells), the new nail may grow back with a different shape or texture.