There should generally be enough room in the toe box to allow your toes to move naturally.
For runners and hikers, it may help to:
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Choose shoes with adequate toe-box space.
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Keep toenails trimmed to a comfortable length.
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Wear moisture-wicking socks that fit properly.
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Avoid suddenly increasing exercise distance or intensity.
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Replace worn-out shoes when their support and fit deteriorate.
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Ensure that the foot does not slide excessively inside the shoe.
If a toenail repeatedly turns black despite correcting footwear, a medical examination can help rule out other causes.
3. Fungal Toenail Infection
A fungal nail infection, medically known as onychomycosis, is another possible explanation for nail discoloration.
Fungi can invade the nail plate and surrounding structures, gradually changing the nail's appearance.
Although fungal infections commonly produce yellow, white, or brown discoloration, some affected nails can develop darker areas that appear brown or nearly black.
The infection may begin at the edge of the nail and gradually spread toward the center.
Other symptoms to recognize
A fungal toenail infection may cause:
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Thickened nails.
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Yellow, white, brown, or dark discoloration.
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Brittle or crumbly nail edges.
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Nails that become distorted.
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Debris collecting underneath the nail.
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Separation of the nail from the nail bed.
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An unpleasant odor in some cases.
Unlike a traumatic bruise, fungal discoloration usually develops gradually.
The nail may become increasingly thick and irregular over time rather than developing one sudden dark patch after an injury.
Why do fungal infections develop?
Fungi thrive in warm, moist environments.
Risk factors include:
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Sweaty feet.
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Wearing damp socks for long periods.
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Walking barefoot in communal showers or swimming pool areas.
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Having athlete's foot.
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Sharing nail clippers or footwear.
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Having diabetes or reduced circulation.
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Having a weakened immune system.
Older adults are also more likely to develop fungal nail infections because nail growth slows and circulation or other health factors may change with age.
How is it treated?
Treatment depends on the severity and the number of affected nails.
A healthcare professional may recommend topical antifungal medication or oral antifungal treatment.
Oral medication is sometimes more effective for extensive infections, but it can have side effects and may interact with other medications.
Laboratory confirmation is often useful before starting treatment because several conditions can resemble fungal nail disease.
Fungal infections can take months to improve because the damaged portion of the nail must gradually grow out.
4. Nail Separation and Dark Discoloration
Another condition that may contribute to a dark toenail is onycholysis.
Onycholysis occurs when the nail plate separates from the nail bed underneath it.
The separated area may appear white, yellow, or discolored because air, debris, and microorganisms can collect beneath the nail.
In some cases, the area may look brown or dark.
Several factors can contribute to nail separation:
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Repeated physical trauma.
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Fungal infection.
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Psoriasis.
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Certain medications.
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Chemical exposure.
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Thyroid disorders.
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Other inflammatory skin conditions.
When the nail separates, the exposed space can become vulnerable to additional irritation or infection.
The condition is not necessarily painful, which means some people may not notice it until the discoloration becomes more obvious.
What should you do?
Avoid pulling off the detached nail.
Keep the area clean and dry, and avoid footwear that places pressure on the affected toe.
If the nail is increasingly separating, changing color, becoming painful, or producing discharge, seek medical assessment.
Treatment depends on the underlying cause rather than the separation itself.
5. Melanonychia: Dark Pigmentation in the Nail
Not every dark toenail is caused by blood or infection.
Sometimes, the nail becomes darker because pigment is being produced within the nail matrix, the area responsible for generating new nail cells.
This condition is known as melanonychia.
It can appear as a brown or black longitudinal band running from the base of the nail toward the tip.
In many people, melanonychia is benign.
Possible causes include:
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Normal variation in pigmentation.
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Genetic factors.
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Aging.
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Repeated nail trauma.
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Certain medications.
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Inflammatory skin conditions.
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Some systemic medical conditions.
People with darker skin tones may naturally develop pigmentation bands in one or several nails.
However, a new or changing dark band in a single nail deserves attention because it can occasionally be associated with nail melanoma.
What changes should you watch for?
Pay particular attention if a dark band:
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Appears suddenly in one nail.
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Becomes wider over time.
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Develops irregular borders.
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Contains several shades of brown or black.
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Extends onto the surrounding skin.
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Causes nail splitting or distortion.
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Changes noticeably without an obvious explanation.
These characteristics do not automatically mean cancer is present, but they justify evaluation by a dermatologist.