While individual nails may on occasion get small white lines or dots, called leukonychia (nothing to worry about), or maybe an infection by bacteria, virus, or fungus (all of which should get treated), an underlying illness somewhere else in your body can also cause changes in nail health and their appearance. Nail care includes watching out for these key changes. 

Decoding Nail Color Changes
The following nail changes are connected to a variety of health conditions:
  • White nail syndrome. The whole nail will appear cloudy or white. This change in nail health could indicate heart disease, renal failure, liver cirrhosis, pulmonary tuberculosis, diabetes, or rheumatoid arthritis.
  • Terry’s nails. The nail will look mostly white and grainy with a pink or perhaps red strip at the top because of an increase in connective tissue and a decrease in blood supply in the nail bed. This change in nail health can be found in 80 percent of patients with liver cirrhosis, as well as in patients with congestive heart failure, hyperthyroidism, malnutrition, diabetes, or HIV.
  • Muehrcke’s nails. Abnormal blood flood in the nail bed will make the nails appear as if they have horizontal (often paired) white lines, most often in the second, third, and fourth fingers. The lines disappear if the nail is pressed and blood is squeezed out of the nail bed blood vessels. Because this problem occurs in the nail bed, it will not progress up as the nail grows. Problems associated with this are hypoalbuminemia, liver disease, malnutrition, and nephrotic syndrome; it is also a side effect of chemotherapy.
  • Half-and-half nails, also known as Lindsay’s nails. The bottom half of the nail appears white while the top half is a darker pink-brown. This is because there is swelling in the nail bed at the bottom and increased melanin (a type of skin pigment) production at the top. Chronic renal disease or HIV could be the cause of this condition.
  • Mee’s line. Horizontal white lines appear in the nail, caused by microscopic fragmentation of the nail after growth has been disrupted. Mee’s lines could indicate heart failure, Hodgkin disease, renal failure, system-wide infection, or poisoning by arsenic, thallium, or other heavy metals.
  • Splinter hemorrhages. These thin, dark red or brown vertical lines in the nail bed look like splinters beneath the nail, hence the name. Possible causes include cirrhosis, mitral stenosis, oral contraceptive use, pregnancy, peptic ulcer disease, scleroderma, rheumatoid arthritis, systemic lupus erythematosus, vasculitis, and trauma. A classic association is with subacute bacterial endocarditis (infection of the heart valves).
  • Yellow nail syndrome. In this rare condition, nails appear yellowish-orange and thicken and curve into the cuticle. It is associated with lymphedema (impaired lymphatic drainage), pleural effusions, and bronchiectasis.
  • Blue nail. Blue nails — either the lunula or the whole nail — could indicate Wilson’s disease, argyria (silver poisoning), or quinacrine therapy (used to treat lupus and other health conditions).
  • Red lunula. Lunulas that appear red could indicate alopecia areata (hair loss), carbon monoxide poisoning, cardiac failure, chronic obstructive pulmonary disease, chronic urticaria (hives), cirrhosis, collagen vascular disease, oral prednisone treatment, or psoriasis.
  • Vertical brown streaks. These are common among people with dark skin; however, they can indicate melanoma and should be checked by a doctor. A benign nevus (overgrowth of cells) or chemical staining (including from some nail polishes) could also be the cause.
Nail Texture Changes
Apart from the odd bump or small lines, nails are normally fairly smooth. But texture can change if there is a problem elsewhere in the body:
  • Beau’s line. When there is a disruption in nail growth, a deep horizontal groove can appear. This could indicate peripheral artery disease, pemphigus (a skin disease), psoriasis, Raynaud’s disease, systemic infection, or trauma.
  • Pitting. Small, pinpoint depressions can appear in the nails when there are problems in nail plate layering. This is seen in 10 to 50 percent of people with psoriasis. It can also be caused by alopecia areata, pemphigus, a type of arthritis called Reiter’s syndrome, and sarcoidosis.
Nail Shape Changes
A wide range of health issues can cause the shape of the nails to change, sometimes radically:
  • Spoon shaped nails (koilonychias). The nails curl up at the edges and become whiter, fragile, and concave. This can have a variety of causes, including iron deficiency anemia, hemochromatosis, hypothyroidism, malnutrition, nail trauma, constant exposure to petroleum-based solvents, Raynaud’s disease, and systemic lupus erythematosus.
  • Clubbed nails or clubbing. The soft tissue around the nail and fingertip becomes enlarged, and the nails become thicker, harder, shinier, and shaped like a bulb, while the flesh below the cuticle gets spongy. Clubbing is usually caused by low oxygen levels in the blood and is associated with lung and heart conditions such chronic obstructive pulmonary disease (COPD), chronic bronchitis, congestive heart failure, and congenital heart disease. It is also seen with liver disease and inflammatory bowel diseases, and can signify cancer, most commonly of the lung and lung lining.
Nail Separation
Certain medical conditions can cause nails to lift off the nail bed:
  • Onycholysis. If the nail separates from the nail bed starting at the top portion of the nail, it can signal medical problems including anemia, certain types of cancer, connective tissue disorders, fungal infection, psoriasis or psoriatic arthritis, reactive arthritis, amyloidosis, sarcoidosis, syphilis, systemic lupus erythematosus, and most commonly, trauma. It can also occur with hyperthyroidism, with the fourth and fifth nails possibly becoming brown.
  • Onychomadesis. The nail separates from the nail bed starting from the base, and usually results in complete loss of the nail. Causes include fungal infection, Raynaud’s disease, chemical damage, frostbite, hand-foot-mouth disease, poor nutrition, febrile illness, and vascular disease, though the most common cause is also trauma.
If your nails start to look different to you in any of the ways described above, consider it a sign to call your doctor.

Source: http://www.everydayhealth.com/skin-and-beauty/beauty/what-your-nails-say-about-you.aspx?pos=1&xid=nl_EverydayHealthBeauty_20140814