Koilonychia - spooning, or nails that grow upwards. Associated with iron-deficiency anaemia or vitamin B12 deficiency. Pitting of the nails is associated with psoriasis. Beaus lines are horizontal ridges in the nail. Habit-tic deformity is a condition similar to Beaus Lines caused by long-term skin picking. Discoloration of entire nail bed
Yellowing of the nail bed is associated with chronic bronchitis, lymphatic problems, diabetes, and liver disorders. Brown or copper nail beds are associated with arsenic or copper poisoning, and local fungal infection. Redness is associated with heart conditions. Other color changes and markings
Melanonychia (longitudinal streaking that darkens or does not grow out), especially on the thumb or big toe, may indicate subungual melanoma. White lines across the nail (leukonychia striata, or transverse leukonychia) may be Mees lines or Muehrckes lines. Small white patches  are known as leukonychia punctata. Dark nails are associated with B12 deficiency. Stains of the nail plate (not the nail bed) are associated with  smoking, and henna use. Splinter hemorrhages (or haemorrhages) are tiny blood clots that tend to run vertically under the nails. Drug-induced nail changes are caused by drug usage which may result in various abnormalities. : 665–6

Treatment
In approximately half of suspected nail fungus cases there is actually no fungal infection, but only some nail dystrophy. Before beginning oral antifungal therapy the health care provider should confirm a fungal infection. Administration of treatment to persons without an infection is unnecessary health care and causes needless exposure to side effects.
Common causes include localized infection, minor injury to the matrix bed, or severe systemic illness. It is sometimes a side effect of chemotherapy or x-ray treatments for cancer. A new nail plate will form once the cause of the disease is removed. Onychomycosis, also known as tinea unguium, is a contagious infection of the nail caused by the same fungal organisms which cause ringworm of the skin (Trichophyton rubrum or T. mentagrophytes, rarely other trichophyton species or Epidermophyton floccosum ). It can result in discoloration, thickening, chalkiness, or crumbling of the nails and is often treated by powerful oral medications which, rarely, can cause severe side effects including liver failure. Mild onychomycosis sometimes responds to a combination of topical antifungal medication, sometimes applied as special medicinal nail lacquer, and periodic filing of the nail surface. For advanced onychomycosis, especially if more than one nail is infected, systemic medication (pills) is preferred. Home remedies are often used, although their effectiveness is disputed. Onychophosis is a growth of horny epithelium in the nail. Onychoptosis is the periodic shedding of one or more nails, in whole or part. This condition may follow certain diseases such as syphilis, or can result from fever, trauma, systemic upsets or adverse reaction to drugs. Onychorrhexis also known as brittle nails, is brittleness with breakage of fingernails or toenails. Paronychia is a bacterial or fungal infection where the nail and skin meet. Koilonychia is when the nail curves upwards (becomes spoon-shaped) due to an iron deficiency.