A toenail that regrows with an abnormal shape, color, or texture is medically referred to as nail dystrophy. Toenail regrowth is a notoriously slow process, relying on the production of healthy cells from the nail root, or matrix, located beneath the skin at the base of the nail. If this “nail factory” is compromised, the resulting nail plate will be deformed, leading to symptoms like thickening, discoloration, ridging, or separation from the nail bed (onycholysis). The cause of this disruption may be physical, infectious, or related to systemic health.
Physical Damage to the Nail Matrix
One of the most common reasons a toenail grows back abnormally is a physical injury to the nail matrix. This damage can result from a single, severe event, such as stubbing a toe or dropping a heavy object, which causes acute trauma. This acute impact often results in a subungual hematoma, or blood under the nail, and the resulting inflammation can permanently scar the cell-producing matrix. A scarred matrix produces a permanently thickened, ridged, or uneven nail structure.
A more subtle, yet equally damaging cause is chronic microtrauma, often seen in athletes or individuals wearing improperly fitting shoes. Repeated, minor pressure from tight footwear or the impact of running causes continuous stress on the nail, particularly the big toe. This continuous force disrupts the matrix’s function, resulting in the production of excessive keratin, which presents as a thickened, distorted, or curved nail (onychogryphosis). In some cases, previous surgical procedures involving the nail, such as aggressive matrix removal to treat a severe ingrown nail, can also lead to permanent distortion or the inability of the nail to grow back completely.
Fungal and Bacterial Infections
Infectious pathogens are a frequent cause of abnormal toenail regrowth, with fungal infections being the most prevalent. Onychomycosis, or toenail fungus, is caused primarily by dermatophytes, which infiltrate the nail plate and the nail bed. These fungi consume keratin, the primary protein component of the nail, leading the nail to react by growing chaotically and producing debris.
A fungal infection typically manifests as discoloration—often yellow, white, or brown—extreme thickening, and a crumbly texture. The buildup of fungal debris under the nail plate, known as subungual hyperkeratosis, pushes the nail up and away from the nail bed, causing it to detach. Because toenails grow slowly, the infection must be fully cleared before a healthy, non-infected nail can fully replace the damaged portion, a process that can take a year or longer.
Bacterial infections can also interfere with regrowth, though they are less common as a primary cause of permanent dystrophy. Pseudomonas aeruginosa is a common bacterium that can colonize the space between the nail and the nail bed, especially if the nail is already separated due to trauma or fungus. This bacterium produces a distinct pigment, causing a greenish or occasionally black discoloration of the nail plate. Although these bacterial infections are typically localized and less likely to permanently damage the matrix than chronic fungus, they indicate a breach in the nail’s natural defense that requires specific treatment.
Underlying Skin and Health Conditions
Sometimes, the cause of an abnormal nail is not localized trauma or infection but a systemic health or dermatological condition affecting cell turnover throughout the body. Psoriasis, an autoimmune condition, commonly affects the nails; up to 90% of people with chronic psoriasis experience some nail involvement. When the disease affects the nail matrix, it can lead to small pits or depressions in the nail surface.
Psoriasis affecting the nail bed causes a yellow-red discoloration known as the “oil drop” or “salmon patch” and the separation of the nail from the bed (onycholysis). Similarly, inflammatory skin conditions like eczema or dermatitis can cause inflammation near the cuticle, which then disrupts the matrix and may result in horizontal grooves or ridges in the nail plate. Treating these nail changes requires managing the underlying systemic condition rather than just focusing on the nail itself.
Other systemic issues, particularly those that compromise circulation, can also impact healthy nail regrowth. Conditions like diabetes or peripheral artery disease reduce blood flow and nutrient delivery to the nail matrix. This lack of resources can lead to slower growth, discoloration, and increased susceptibility to secondary infections like onychomycosis, further compounding the nail’s abnormal appearance.
When to Seek Professional Diagnosis and Treatment
Professional help is often necessary to identify the exact cause of an abnormal toenail and determine effective treatment. You should consult a specialist, such as a podiatrist or dermatologist, if the nail abnormality is accompanied by pain, swelling, or redness, which are signs of an active infection. Persistent, worsening symptoms or uncertainty about the cause also warrant a professional evaluation, especially if you have an underlying condition like diabetes that increases the risk of complications.
Specialists can perform diagnostic tests, such as scraping the debris under the nail for a fungal culture or a potassium hydroxide (KOH) examination, to definitively identify a fungal infection. Treatment may involve oral or high-concentration topical antifungal medications, or thinning the thickened nail with specialized instruments to relieve pressure and improve appearance. For abnormalities caused by inflammatory conditions, treatment focuses on managing the underlying disease with targeted therapies. Severe, chronically ingrown nails or those damaged by irreversible trauma may require surgical intervention to permanently correct the growth pattern.