Green, blue, black, yellow fingernails can have various causes, ranging in severity from 'minor' to 'generally fatal'. 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 green, blue, black, yellow fingernails, we could:
|Congestive Heart Failure||17%||Unlikely|
|Chronic Bronchitis||0%||Ruled out|
|Pulmonary Embolism||0%||Ruled out|
|Ochronosis / Alkaptonuria||0%||Ruled out|
|Fungal Infection||0%||Ruled out|
Are (parts of) your fingernails any unusual color other than white?
Possible responses:→ No / another color (add a note) / don't know
→ Green / greenish
→ Blue / bluish
→ Black / somewhat brown
→ Yellow / yellowish
Black nails (melanonychia) can be a medication side-effect, particularly of cyclophosphamide (Cytoxan).
Black line(s) across the nails are common in dark-skinned persons but may also be the result of injury or chemotherapy.
Green nails are generally due to a Pseudomonas pyocyanea infection. One of the most common causes of yellow nails is a fungal infection. Black nails are a possible indication of bacterial or fungal infection.
Black nails are sometimes seen in people infected with AIDS.
A longitudinal brown-black streak (which may take up the whole nail and may "spill over" into the proximal nail fold) is a sign of melanoma, and possibly Hutchinson's.
Nails with a bluish tint can mean the body isn't getting enough oxygen. This could indicate an infection in the lungs, such as pneumonia.