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Thickened
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Brittle
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Discolored
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Cracked
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Crumbly
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Detached from the nail bed
Although fungal infections are more common in toenails, fingernails can also be affected.
The important point is that not every damaged nail is caused by fungus. Using antifungal treatments without knowing the cause may not solve the problem.
What If the Nail Is Lifting?
The photograph also appears to show an irregular edge where the nail may be separating from the skin underneath.
This is known as onycholysis.
Nail separation can occur because of trauma, repeated irritation, fungal infection, certain skin conditions, or other factors.
Once the nail lifts, moisture and debris can become trapped underneath it, potentially making the nail look darker or dirtier.
If the separation continues or keeps returning, it's worth having the nail examined.
Pay Attention to Dark Pigmentation That Doesn't Go Away
There is another reason persistent dark nail discoloration shouldn't automatically be dismissed as a bruise.
In rare cases, a dark streak or patch beneath a nail can be associated with subungual melanoma, a form of melanoma that develops around the nail unit.
Most dark nails are not melanoma. A previous injury, pigmentation, infection, and other conditions are much more common explanations.