The appearance of fingernails can tell a doctor many things about a person's health, from a simple vitamin deficiency to something more serious. There are many causes of grooves or ridges on fingernails. Vertical grooves or ridges are quite common; however, horizontal ridges are not and they may signify an underlying illness. Consult your doctor should you discover horizontal ridges on your fingernails.

Beau's Lines

Beau's lines are horizontal depressions on the fingernail, usually at the same area on the nail plate. They occur after or during a serious illness such as a systemic infection or diabetes. Cancer patients being treated with chemotherapy may get Beau's lines. Patients with Raynaud's disease may get horizontal ridges on their fingernails from being exposed to cold temperatures. Nail trauma and malnutrition can also cause Beau's lines. The grooves may disappear after recovering from illness.

Muehrcke's Lines

Muehrcke's lines appear as pairs of transverse white lines extending horizontally across the nail, parallel to the lunula. These grooves are caused by a vascular abnormality in the nail bed and disappear temporarily when the nail is pressed. Muehrcke's lines do not occur in the nail bed, therefore, they do not move with growth of the nails. These fingernail lines are prevalent in patients with low albumin levels, kidney or liver disease and malnutrition.

Mee's Lines

Mees' lines are horizontal, white bands on multiple nails caused by arsenic poisoning or, rarely, serious systemic illnesses. The width of these fingernail lines can vary. As the nail bed itself is not affected, Mees' lines move higher as the nail grows.

Terry's Nails

In Terry's nails, the nail plate is white except for a narrow horizontal band near the finger tip. These horizontal ridges on the fingernails are sometimes seen in patients with liver cirrhosis, diabetes, kidney disease or HIV infection.

Horizontal Half Moons (Lunulae)

The white, horizontal, half-moon shape that appears at the base of some nail beds (most commonly on the thumb and forefinger nails) is called the lunula. If the lunulae are blue in color, this may represent Wilson Disease or silver poisoning. Red lunulae can be caused by liver cirrhosis, carbon monoxide poisoning, COPD, heart failure or psoriasis.

Nail Trauma

Nails can sustain horizontal dents or ridges from physical trauma to the nail bed. If you discover horizontal ridges on your fingernails, consider any recent trauma as the cause. These grooves are typically temporary and will grow out with the nail.