The most common causes of nail discoloration include fungal infections, bacterial infections caused by pseudomonas, and hematoma due to trauma, according to MedicineNet. Liver, lung, kidney and heart conditions may also cause nail discoloration and other changes in nail appearance.
Approximately half of all nail discoloration cases are due to fungal infections, states MedicineNet. The most common fungus to affect the nails is Trichophyton rubrum, a dermatophyte that normally infects the skin. The shade of discoloration ranges from milky white to brown, and additional symptoms of a fungal infection include thickening, spotting and streaking of the nails, according to eMedicineHealth. Fungal infections are normally painless, but excessive thickening of the nails may cause difficulty walking and standing.
If the nails have experienced recent trauma, they may appear red or black as blood collects under the nail bed in a hematoma, explains MedicineNet. Ingrown nails can also cause this type of discoloration. Pseudomonas infections of the nail bed can result in a green tint to the nails. The Centers for Disease Control and Prevention cite antibiotics as the main treatment for pseudonomas infection. To prevent future infections, patients should practice good hand hygiene and avoid contact with poorly maintained hot tubs and pools.