The sudden appearance of a secondary growth beneath the primary toenail can be a confusing discovery. This phenomenon, which can feel like a new nail plate emerging from underneath the existing one, suggests an underlying physical change in the nail unit. Identifying the nature of this growth is the first step toward understanding and resolving the issue.
Understanding the Potential Causes
The sensation of a second nail forming often results from an abnormal physical mass displacing the nail plate from below. One frequent cause is subungual exostosis, a benign outgrowth of bone and cartilage arising from the distal phalanx (the bone at the tip of the toe). This bony spur typically occurs on the great toe and slowly pushes the nail upward as it grows. This growth causes pain and a firm nodule often mistaken for a second nail. While the precise cause is unknown, it is often associated with prior trauma or chronic irritation to the area.
Another possibility is onychomatricoma, a rare, non-cancerous soft tissue tumor originating from the nail matrix. Unlike exostosis, this tumor actively produces an abnormal nail substance. Onychomatricoma causes distinct changes, including significant nail plate thickening, yellowish discoloration, and characteristic longitudinal grooves or channels. The tumor is composed of finger-like projections that embed themselves into the nail plate, leading to the distorted appearance of a secondary growth.
The appearance of a nail under a nail can also result from true nail duplication or a condition called retronychia. Retronychia occurs when the nail plate stops growing outward and instead grows backward into the proximal nail fold. This leads to stacked layers of new nail plates underneath the old one. This condition is a direct response to trauma, often from poorly fitting shoes or an injury that disrupts the alignment between the nail matrix and the nail bed. The pressure from the backward-growing nail pushes the original nail upward, creating the illusion of two separate growths.
The Necessity of Professional Diagnosis
Since a secondary growth can represent vastly different underlying conditions—ranging from bone spurs to tumors or trauma-induced duplication—a medical evaluation is necessary. Attempting self-treatment or trying to cut out the growth can be dangerous, especially if the mass is vascular or involves the underlying bone structure. A podiatrist or dermatologist specializing in nail disorders is the most appropriate professional to consult.
The diagnostic process begins with a detailed physical examination and a review of the patient’s medical history, particularly any history of trauma. If a bony cause like subungual exostosis is suspected, an X-ray is the standard tool. The X-ray confirms the presence and size of the osseous outgrowth and determines if the mass is a dense bone spur growing from the phalanx.
If a soft tissue tumor, such as onychomatricoma, is suspected, imaging techniques like ultrasound or magnetic resonance imaging (MRI) can visualize the internal structure of the mass. These tools determine its relationship to the nail matrix. The definitive diagnosis for any tumor or atypical growth often requires a biopsy, where a small tissue sample is taken and analyzed under a microscope. Histopathology confirms the exact cellular nature of the growth, which is necessary to rule out rare but aggressive conditions.
Treatment and Removal Procedures
Once a professional diagnosis is established, treatment protocols are tailored to the specific nature of the growth. For subungual exostosis, surgical removal is the standard approach to alleviate pain and pressure. The procedure is typically performed under local anesthesia, often using a digital block to numb the entire toe.
The surgeon removes the nail plate, excises the bone spur, and often scrapes the underlying bone (curettage) to minimize the risk of recurrence. Recovery involves keeping the wound clean and elevated. Most patients return to normal activities within one to two weeks, though the nail may take many months to regrow completely.
For onychomatricoma, complete surgical excision is required to remove the tumor and prevent recurrence. This procedure involves carefully removing the tumor from the nail matrix. The goal is to excise the entire abnormal tissue while preserving the surrounding healthy nail matrix to allow for normal nail regrowth.
For conditions like retronychia, treatment may begin with non-surgical methods, such as wearing wider footwear to eliminate chronic pressure. If multiple layers of stacked nail have formed, surgical avulsion (removal of the entire affected nail plate) is often required. This resolves the issue and allows the nail unit to reset and grow a single, healthy plate. Regardless of the condition, surgical intervention generally offers a definitive resolution, though a small risk of recurrence exists depending on the completeness of the removal.