Yes, you can use the gel on dry skin on your hands, and it can also be applied to nails at least once a day. (Podiatrists often advise using urea in tandem with antifungal treatments because it softens the nail bed so that antifungals can penetrate more deeply.)
It's also really helpful to use a good, rich moisturizing cream (our Shea Butter Skin Repair Cream is ideal) on top of the gel for best results. Nail ridges have many different causes (aging, trauma, etc.) most all of which are helped by moisturizing, and creams with urea are often recommended.