The most common reason for discolored nails is fungal infections causing a condition known as onchymycosis. Not just discoloration, it also leads to thickening and deformation of nails. Common oral drugs used for treatment of onychomycosis are griseofulvin, terbinafine, itraconazole and ketoconazole. Application of anti-fungal nail lacquers is also an effective solution. Apart from this, it is important to follow general precautions like keeping the nails dry, using sanitized instruments for manicure and avoiding nail biting.