Beau's lines are multiple horizontal grooves in the fingernails that run parallel to the base of the nail bed. These lines happen when cells in the nail matrix temporarily stop dividing, triggered by an illness or bodily trauma. Beau's lines should be distinguished from vertical ridges that run from the base of the nail to the tip, which often become prominent with age and are typically not a health concern.
Nails are made of layers of keratin, a protein also found in the skin and hair. Nail growth happens as a result of normal cell division, when the older cells are pushed out toward the fingertips by the production of new cells. Horizontal grooves in the nails, commonly called Beau's lines, indicate an interruption of this process due to a trauma. This trauma could be local, affecting only the nail and surrounding area, or systemic, related to an experience or condition that affects the entire body system. Common traumas that could result in Beau's lines or other nail inconsistencies include surgery, chemotherapy, severe illness, or a physical injury to the nail bed.
In contrast to the horizontal grooves called Beau's lines, vertical ridges in the nail are usually not a cause for concern. Vertical ridging, which appears perpendicular to the nail bed, is typical with advanced age and could have a hereditary basis. Any type of horizontal ridge or grooves, or any changes in nail color, should be investigated by a doctor as a possible indicator of an underlying medical condition such as malnutrition, respiratory disease, or heart problems.
Healthy nails appear consistent and smooth. White spots on the nail are generally caused by minor nail trauma and will grow out as the nail grows. Other inconsistencies could be indicators of a medical condition. Signs that should be reported to a doctor include discoloration, curling or pitting of the nail, or separation of the nail from the nail bed.
Beau's lines are named for the French physician Joseph Honore Simon Beau, who first described the condition. A German physician, Johann Christian Reil, also contributed to the medical literature on this condition. Thus, Beau's lines are sometimes called Beau-Reil cross furrows.