Dark lines under fingernails can have various causes, just like most other symptoms. Finding the true cause means ruling out or confirming each possibility – in other words, diagnosis.
Diagnosis is usually a complex process due to the sheer number of possible causes and related symptoms. In order to diagnose dark lines under fingernails, we could:
Research the topic
Find a doctor with the time
Use a diagnostic computer system.
The process is the same, whichever method is used.
Step 1: List all Possible Causes
We begin by identifying the disease conditions which have "dark lines under fingernails" as a symptom. For example, melanoma.
Step 2: Build a Symptom Checklist
We then identify all possible symptoms and risk factors of each possible cause, and check the ones that apply:
melanoma in family members
having many common moles
lighter/paler skin color
very many irregular dark moles
light eye color
history of melanoma
... and so on
Step 3: Rule Out or Confirm each Possible Cause
A differential diagnosis of your symptoms and risk factors finds the likely cause of dark lines under fingernails.
Arriving at a Correct Diagnosis
The Analyst™ is our online diagnosis tool that learns all about you through a straightforward process of multi-level questioning, providing diagnosis at the end.
Do you have any dark lines/streaks below the nails, running in the direction of nail growth?
→ No / don't know
Based on your response to this question, which may indicate dark lines under nails, The Analyst™ will consider possibilities such as Melanoma. Dark lines beneath the nail should be investigated as soon as possible.