Nails are composed of layers of protein called keratin. The nail grows outward from the base of the nail or nail matrix which is under the cuticle. The nail plate is the actual fingernail or toenail. The nail bed is the skin under the nail plate. Systemic diseases cause disorders in nails. Psoriasis and fungal infections are two diseases that cause changes in the appearance of fingernails and toenails.
Ridges
Vertical ridges which form from the cuticle to the top of the nail are part of the normal aging process. Horizontal ridges that appear across the entire nail are a sign of a health issue. Muehrcke lines are white horizontal lines that appear in pairs on the fingernails. This disorder is associated with malnutrition, chronic renal failure and liver disease. Beau's lines are horizontal indentations that occur on the nails. This disorder is caused by an interruption in nail growth because of an illness, disease or trauma. Mee's lines are horizontal white bands which appear on fingernails and toenails after poisoning with arsenic or carbon monoxide.
Discoloration
Yellow nail syndrome is a disorder characterized by slow nail growth, thickening of the nail plate and yellow nail color. It is associated with chronic sinusitis, rheumatoid arthritis and immunodeficiency. Azure lunula is a disorder affecting the lunula, which is the crescent shaped white area at the base of the fingernail. This disorder is associated with Wilson's disease in which the body retains too much copper. Only the lunula turns blue. A red lunula indicates the presence of heart disease.
Psoriasis
Psoriasis affects the normal growth of the nails and causes deep pitting of the nails. Yellow to yellow-pink discoloration of the nails results when the disease affects the nail bed. The nail plate can pull away from the nail bed. White areas under the nail plate are a sign that this is happening. The skin surrounding the nail may be reddened. Psoriatic involvement of the nail matrix causes yellow patches to form on the nail plates. These patches crumble and the entire nail may fall off.
Fungal Infections
Onychomycosis is a fungal infection that affects the nails. Fungus, yeasts and mold are microscopic organisms that cause nail fungal infections. They can enter through tiny cuts in the skin or a small separation between the nail and nail bed. These organisms thrive in warm moist environments. For this reason, fungal infections are more common in toenails. A small white or yellow dot under the tip of the nail is the first sign of a fungal infection. The affected nail becomes thicker than normal, distorted in shape, and dull. Pain in the toes or fingers and a foul odor are associated with a fungal infection of the nails.
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