5 Tips to Prevent Black Toenails from Running

Black toenails are experienced by runners at every level, from weekend warriors to marathon veterans. At Align Foot & Ankle Center in Camarillo, California, board-certified podiatrist Hai-En Peng, DPM, FACFAS, sees runners who develop these painful nail injuries that can sideline training for weeks.

Don’t just assume black toenails simply come with being a runner. Here are five prevention strategies that can keep your nails healthy while you chase your mileage goals.

1. Buy running shoes a half-size larger than your regular shoes

Running causes your feet to swell as blood flow increases and impact forces accumulate. Your feet can expand up to a half-size during extended runs, creating pressure that drives toenails against shoe fronts.

Aside from buying slightly larger running shoes, try shopping in the afternoon or evening when your feet are naturally swollen. Leave at least a thumb’s width of space between your longest toe and the shoe front. This extra room prevents repeated nail trauma that develops into black spots over multiple runs.

2. Use heel lock lacing for downhill sections

Steep descents force your feet to slide forward inside your shoes with each step. Even properly fitted shoes can’t prevent this forward momentum completely. Your toes repeatedly jam against the front of the shoe, creating the repetitive trauma that leads to black nails.

Trail runners and those training on hilly terrain face higher black toenail risk than flat-course runners. The angle of descent determines impact severity. A gradual decline over several miles often causes more damage than a short, steep hill because the repetitive sliding motion continues longer.

Learn the “heel lock” or “runner's loop” lacing technique before tackling hilly routes. This method creates additional heel stability, reducing forward foot movement inside the shoe. 

3. Run on softer surfaces at least twice per week

Concrete creates different stress patterns than asphalt, trails, or tracks. Hard surfaces like sidewalks don’t absorb impact forces, transferring more energy through your feet to your toenails. The constant pounding on unforgiving surfaces accelerates nail bed damage.

Plan your runs on softer surfaces like trails, tracks, or even well-maintained grass fields. This approach distributes stress patterns differently and gives overused nail beds time to recover between high-impact sessions. 

4. Choose shoe shapes that match your toe pattern

People with longer second toes (Morton’s toe) experience black nail problems in different locations than those with longer big toes. Your toe length determines which nails take the most abuse during running.

Standard shoe designs assume your big toe is the longest, but many people have longer second toes. These runners often develop problems in their second toenail while their big toe remains unaffected. Shoe selection needs to account for your specific toe length pattern.

5. Follow the 10% rule when increasing weekly mileage

Rapidly increasing running distance overwhelms your feet. Nail beds need time to develop tolerance to repetitive pressure, just like muscles and joints need gradual conditioning.

The 10% weekly mileage increase rule applies to nail health as much as injury prevention. Sudden jumps in distance or intensity create more nail trauma than steady, progressive training increases.

Track your weekly mileage and resist the urge to make dramatic increases, even when you feel strong. If you ran 20 miles last week, limit this week to 22 miles maximum. 

Get specialized running injury care in Camarillo, California

Black toenails can signal underlying biomechanical issues that affect your entire running performance. At Align Foot & Ankle Center, Dr. Peng provides comprehensive evaluations for runners dealing with recurring nail problems.

Contact our Camarillo office today to schedule a consultation and keep your running goals on track.