Unusual Colors Of Fingernails

What Causes Green, Blue, Black, Yellow Fingernails?

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:
  • 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 "green, blue, black, yellow fingernails" as a symptom.  Here are eight of many possibilities (more below):
  • Pulmonary Embolism
  • Pneumonia
  • Chemotherapy Side-Effects
  • Lung Cancer
  • Ochronosis / Alkaptonuria
  • Diabetes II
  • Melanoma
  • Congestive Heart Failure

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:
very low HDL cholesterol level
taking naps
light hair
recent onset nausea
recent productive cough
difficulty losing weight
having very many common moles
constant fatigue
occasionally feeling unusually cold
long menstrual cycles
high systolic blood pressure
diabetes in family members
... and more than 60 others

Step 3: Rule Out or Confirm each Possible Cause

A differential diagnosis of your symptoms and risk factors finds the likely cause of green, blue, black, yellow fingernails:
Cause Probability Status
Chemotherapy Side-Effects 96% Confirm
Lung Cancer 26% Unlikely
Pneumonia 13% Unlikely
Pulmonary Embolism 3% Ruled out
Melanoma 3% Ruled out
Ochronosis / Alkaptonuria 1% Ruled out
Congestive Heart Failure 1% Ruled out
Diabetes II 1% Ruled out
* This is a simple example to illustrate the process

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.

If you indicate abnormal fingernails and toenails, The Analyst™ will ask further questions including this one:
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
Based on your response to this question, which may indicate green/greenish fingernails, blue/bluish fingernails, black/brown fingernails or yellow/yellowish fingernails, The Analyst™ will consider possibilities such as:
(Prescription) Drug Side-Effects

Black nails (melanonychia) can be a medication side-effect, particularly of cyclophosphamide (Cytoxan).

Chemotherapy Side-Effects

Black line(s) across the nails are common in dark-skinned persons but may also be the result of injury or chemotherapy.

Fungal Skin / Nail Infection

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.