Corrugated nails, also called nail corrugation or ridged nails, are ridges that can either run longitudinally or appear crosswise on fingernails or toenails, states Right Diagnosis. Horizontal grooves that form in the nail plate are known medically as Beau's lines. This type of nail ridging is often indicative of an underlying serious medical condition or an adverse effect from certain medications.
Nail ridges that run lengthwise from the tip down to the cuticle are typically associated with the aging process and do not pose serious health risks, notes Mayo Clinic. These indentations usually increase in number or become more pronounced with age. The condition is generally attributed to changes in the replacement of old cells with newly produced cells within the affected nail.
Beau's lines are characterized by transverse nail ridging that form parallel depressions to the crescent shape of the nail bed. This condition is mainly due to an irregular interruption of the keratin production process brought on by several causes. Beau's lines may be caused by an injury or a localized disease that damages the nail fold, according to Skinsight. When Beau's lines are visible in the nail plates of all nails in roughly the same spot, a major illness that affects several organs of the body may be the cause. The appearance of Beau's lines is also associated with an adverse response to drugs involved in chemotherapy.