What causes staining of nails?

Dear Doctor,
My two big toe nails seem to be turning black in colour. I noticed this three weeks ago and didn’t think much of it. They keep getting darker, though there is no pain. What could this be? Simon

Dear Simon,

You didn’t mention your age, also, did the discolouration of the two toe nails start simultaneously or one followed the other; is it progressing? 


One of the most common causes of nail discoloration is a fungal infection. Fungi present in the air, dust and soil can infect skin as well as nails. This causes a brownish, blackish discolouration, which usually increases progressively. Bacterial infection of the nail as that caused by pseudomonas can cause greenish colouration of the nail bed, making the nails look black.


Cutting off of blood supply of the nails due to trauma can impart a black discolouration. It can also happen due to chronic ischemia as with old age. Chronic smokers can develop blueish or blackish discoloration of nails, along with that of the tongue due to chronic oxygen deficiency in the body. Similarly chronic lung diseases also cause discolouration of nails. Malnutrition is yet another cause of blackish discolouration of nails. Liver, kidney or heart disorders can cause discoloured nails. It can also be due to diabetes.


Stains caused due to nail paints or nail varnish may leave a residual black colouration. Drugs like tetracycline can cause it as an adverse effect. It may be due to an inherited condition called “yellow nail syndrome”.

Nails which get discoloured due to a chronic infection or sickness can eventually be damaged beyond repair and fall of. Treatment of nail discolouration depends on the cause, which can be identified by suitable investigations.  Fungal infection of the nails can take as long as six to nine months to be cured, because the antifungal agents do not penetrate the nail readily. Hence, one has to have patience.  

Dr Rachna Pande  is a specialist in internal medicine at Ruhengeri Hospital

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