What causes these vertical ridges in my fingernails?

Many reasons: Vertical ridges on nails are basically harmless & can be related to heredity, aging, & nail dryness or injury. The appearance of ridges may be reduced by regular moisturizing of the nail & cuticle & avoidance of harsh soaps that are drying. Nail appearance can reflect overall health and nutrient status so supplementation may help. Consider fish oil, biotin, &/or a multivitamin with minerals.

Dryness: Vertical ridges in fingernails are usually from dryness. Try to avoid waterworking as much as possible or wear rubber gloves. Frequent hand washing can dry out nails. Biotin may help.

Longitudinal Ridges: Longitudinal ridges (running from the cuticle to the free edge of the nail) may be due to aging and not a sign of any disease.