Fingernails and toenails are composed of translucent keratin proteins and various sulfur-containing fibrous proteins, which also form the chemical basis of hair and skin. Healthy nails are consistent in shape and uniform in color. Abnormal color, shape, texture or thickness of the fingernails or toenails indicates a nail disorder. An affected nail can also be a symptom of several other serious diseases, including lung, kidney and liver diseases, as well as diabetes and anemia, according to MedlinePlus.
In psoriasis, a chronic inflammation of the skin, the circulating T lymphocytes--types of white blood cells--on the skin show increased levels of activation with enhanced cytokine, an immunoregulatory protein, secretion. Imbalanced cytokine production stimulates the proliferation of cultured human keratinocytes, or epidermal cells that synthesizes keratin. Nail involvement is common in psoriasis. It may cause detachment of the nail plate from the nail bed, which may result in a permanent nail dystrophy or chronic destruction of the nail plate, notes the University of Maryland Medical Center.
Onycholysis is the separation of the nail plate off the nail bed most commonly due to a fungal or yeast infection. An infection with bacteria and yeast normally occurs in the matrix of the nail, which is the nail part under the cuticle. These pathogens digest the keratin protein of the nail, changing its texture, shape and color. Organic debris begins to accumulate under the space of the nail plate. The nail plate eventually separates from the nail bed and crumbles off.
Koilonychia is characterized by nails that are spoon shaped. People who experience koilonychia are often diagnosed with iron deficiency anemia, a type of anemia that is caused by the lack of iron to create red blood cells. In the early stages of koilonychia, the nails are flattened and have concavities. Later, the nails have raised ridges and appear thin and concave, according to the University of Michigan Medical Center.