Blue nails, or more formally azure lunula, are characterized by a blue discoloration of the lunulae, seen in argyria

Argyria

Argyria is a condition caused by improper exposure to chemical forms of the element silver, silver dust, or silver compounds. The most dramatic symptom of argyria is that the skin becomes blue or bluish-grey colored. Argyria may be found as generalized argyria or local argyria...

 and cases of hepatolenticular degeneration (Wilson's disease), also having been reported in hemoglobin M disease and hereditary acrolabial telangiectases.

In Wilson's disease the blue color involves the lunula (most intense pigmentation) and fades proximally. In argyria

Argyria

Argyria is a condition caused by improper exposure to chemical forms of the element silver, silver dust, or silver compounds. The most dramatic symptom of argyria is that the skin becomes blue or bluish-grey colored. Argyria may be found as generalized argyria or local argyria...

, the nail is permanently pigmented a slate-blue color and is most evident in the lunula. Minocycline

Minocycline

Minocycline is a broad-spectrum tetracycline antibiotic, and has a broader spectrum than the other members of the group. It is a bacteriostatic antibiotic, classified as a long-acting type...

 can also turn the nail plate blue-gray.

Trivia

In season 6 of House MD

House (TV series)

House is an American television medical drama that debuted on the Fox network on November 16, 2004. The show's central character is Dr. Gregory House , an unconventional and misanthropic medical genius who heads a team of diagnosticians at the fictional Princeton-Plainsboro Teaching Hospital in...

 in the episode 11 titled Remorse

Remorse (House)

"Remorse" is the twelfth episode of the sixth season of House. It aired on January 25, 2010.- Plot :The team takes on the case of 27-year-old Valerie , an attractive business consultant experiencing intermittent episodes of excruciating ear pain...

, House diagnoses his patient with Wilson's Disease in absence of Kayser-Fleischer rings

Kayser-Fleischer ring

Kayser-Fleischer rings are dark rings that appear to encircle the iris of the eye. They are due to copper deposition as a result of particular liver diseases. They are named after Dr Bernhard Kayser and Dr Bruno Fleischer, the German doctors who first described them in 1902 and 1903...

 by removing the nail polish to note the blue nails.

See also

• Nail Anatomy
  Nail (anatomy)
  A nail is a horn-like envelope covering the dorsal aspect of the terminal phalanges of fingers and toes in humans, most non-human primates, and a few other mammals. Nails are similar to claws, which are found on numerous other animals....
  
  
• Nail Diseases
• Wilson's Disease
  Wilson's disease
  Wilson's disease or hepatolenticular degeneration is an autosomal recessive genetic disorder in which copper accumulates in tissues; this manifests as neurological or psychiatric symptoms and liver disease...