A broken toenail, which includes horizontal splitting (onychoschizia), occurs when the nail’s protein structure—keratin—is compromised. The break can range from a minor split to a full fracture. It is caused by a single, acute impact or by chronic weakness stemming from underlying health issues. Understanding these causes is the first step toward proper care and prevention.
Physical Causes: Acute Trauma and Pressure
Sudden, forceful injuries are the most direct cause of a broken toenail, often resulting in immediate pain and bleeding. This acute trauma typically involves striking the toe against a hard object, such as stubbing it on furniture, or experiencing a crush injury from a heavy item dropped onto the foot. The intense external force overwhelms the nail’s structural integrity, causing it to crack or split.
Beyond a single severe impact, repetitive micro-trauma is a frequent culprit, especially for active individuals. Activities like long-distance running or playing sports cause the toenail to repeatedly strike the inside of the shoe. This constant, low-level pressure creates a shearing force between the nail plate and the nail bed, which can lead to loosening, bruising, or fracture.
Ill-fitting footwear significantly contributes to this repetitive stress. Shoes that are too short force the nail to jam against the toe box with every step. Overly loose shoes allow the foot to slide forward, causing the toes to repeatedly hit the shoe’s front. This persistent friction and pressure weaken the keratin layers, making the nail brittle and highly susceptible to breaking.
Health Factors That Lead to Nail Weakness
While trauma causes immediate breaks, chronic health conditions can pre-weaken the nail, making it brittle and prone to splitting. Fungal infections (onychomycosis) are a common biological factor that compromises the nail’s structure. The fungi secrete keratinolytic enzymes, which actively degrade the hard keratin protein of the nail plate. This results in a thickened, crumbly, and discolored nail that easily fractures or peels.
Systemic conditions impact the health of the nail matrix, the root where the nail is formed. Thyroid disorders, such as hypothyroidism, can reduce blood flow and nutrient delivery to the nail, resulting in slow growth and brittleness. Psoriasis, an autoimmune skin condition, can cause the nail to lift (onycholysis), develop pitting, or become brittle due to inflammation. Anemia, particularly iron-deficiency anemia, is linked to weakened nails and can manifest as koilonychia, or “spoon-shaped” nails, that are thin and break easily.
Nutritional status plays a direct role in maintaining keratin strength. Biotin, a B vitamin, is a cofactor in keratin production, and a deficiency can lead to brittle nails and splitting. Deficiencies in minerals like iron, zinc, and magnesium also contribute to nail fragility. Environmental factors, such as constant cycles of wetting and drying, severely weaken the nail by causing the keratin layers to expand and contract, leading to lamellar splitting or peeling.
Immediate First Aid for a Broken Toenail
If a toenail breaks, gently clean the injured area with mild soap and water to prevent infection. If there is bleeding, apply light, sustained pressure with a clean cloth or sterile gauze until it stops. Elevating the foot can help reduce throbbing.
If the nail is partially detached, safely trim away the loose or jagged portion using clean clippers or scissors to prevent snagging. Do not attempt to pull off the remaining nail, as this can damage the nail bed underneath. Apply an over-the-counter antiseptic or antibiotic ointment to the exposed nail bed.
Cover the injury with a sterile, non-stick bandage to protect the sensitive nail bed until the nail begins to regrow. Change the dressing daily, or whenever it becomes wet or dirty, to maintain a clean healing environment. Pain and swelling can be managed by applying an ice pack wrapped in a thin towel for short intervals.
When a Broken Nail Requires a Doctor’s Visit
While minor breaks can be managed at home, professional medical attention is necessary if certain signs appear. Seek care if the injury results in severe, persistent pain or if the toe shows signs of infection. These signs include increasing redness, swelling that spreads beyond the toe, warmth, or the presence of pus or foul odor.
A doctor should evaluate any break that exposes a large portion of the nail bed or involves the cuticle area. Bleeding under the nail (subungual hematoma) that covers more than half of the nail plate should be assessed, as draining the pooled blood may be necessary to relieve pressure and pain. Finally, if toenails repeatedly break despite proper care, or if you notice chronic discoloration or thickening, a medical diagnosis is needed to rule out an underlying issue.