Nails may be grooved in two directions: from side to side or from the cuticle outward. When the grooves are from the cuticle outward, they are called longitudinal grooves of the nail, and these are most commonly caused by a cyst, or a little growth in the skin next to the proximal nail fold. To treat this type of cyst, called a myxoma, some form of surgery is typically performed.
When the grooves are from side to side, which is by far more common, they are referred to as Beau’s lines. The most common cause of this disorder is a yeast infection of the skin around the cuticle. This infection injures the nail matrix; because of this type of injury, the matrix cannot produce a smooth nail but instead produces a grooved one. Considering that your client is in good health and not on any medication, a doctor must first provide a diagnosis and treatment. If it is the common yeast infection, then it can be treated with antifungal cream or pills. — Dr. Scher