There are many human nail diseases. According to MedlinePlus, toenails and fingernails consist of multiple layers of the protein keratin, hard substance that provides protection to the toes and fingers. Nails typically are smooth and consistent in color; it's important for nail health to keep them clean, dry and trimmed. Nail diseases occur in both the toes and the fingers.
Onychomycosis
Onychomycosis is a disease associated with human nails. According to MayoClinic.com, onychomycosis, also known as fungal nail infection, occurs when fungi invade one or more of the nails. A fungal nail infection often begins as a white or yellow spot under the tip of a fingernail or toenail. As the nail fungus moves further into the nail, MayoClinic.com says it can cause the nail to change color, thicken and develop ragged edges. Fungal nail infections can be extremely difficult to treat and infections often return. Common signs or symptoms associated with fungal nail infections include thickened, brittle, crumbly or ragged nails, nails that are an unusual shape, that appear dull and are dark in color.
Onychoschizia
Onychoschizia is a disease associated with human nails. The American Osteopathic College of Dermatology states that onychoschizia, or splitting of the fingernails, is one of the most common complaints seen and treated by dermatologists. Onychoschizia is more common in women, with the most common cause being repetitive wetting and drying of the fingernails. This makes the nails dry and brittle--a situation that's typically worse in the winter months, when humidity is lower. The AOCD recommends that a person be gentle with her nails, using a file to round the tips of her nails into a gentle curve. Nails should be filed daily to avoid ragged edges that could lead to more breakage or splitting.
Onycholysis
Onycholysis is another disease associated with human nails. According to the AOCD, onycholysis is the painless separation of a person's nail from the nail bed. It is a common problem seen and treated by dermatologists. Onycholysis may be caused by skin disease, infection or traumatic injury, although most cases of onycholysis occur in women with long fingernails--the longer-than-usual nails are more easily pried away from the skin. The AOCD states that the most common cause of onycholysis is a local irritiation due to excessive filing, chemical exposure during manicures, allergic contact dermatitis, the use of nail hardeners and sustained immersion in water. Regardless of the cause, onycholysis typically affects multiple nails, allowing bacterial and yeast infections to manifest beneath the nail, turning at least a part of the nail white, yellow or green.
