Nail conditions can include distortion and/or discoloration of the normal nail plate on the fingernails and toenails. Washboard nails appear as grooves and ridges in the center of your thumb; thin, spoon-shaped nails dip down in the middle and look like spoons; and pitted nails with dents look like they were made by an icepick.
Discoloration can include a new or changing dark streak, which could be melanoma, the most serious type of skin cancer. However, not every dark streak is a melanoma. Nail fungus, an infection of the nail, can also cause discoloration. It begins as a white or yellow-brown spot under the tip of your fingernail or toenail, and may include debris under the nail and thickening nails.
According to the Centers for Disease Control and Prevention (CDC), fungal nail infections are very common and may affect up to 14% of the U.S. population; fungal toenail infections are more common than fungal fingernail infections.