Like your skin, nails (which are made of keratin and water) "have a harder time holding onto moisture in your 30s," says N.Y.C. dermatologist Joshua Zeichner. In addition to applying a daily hydrating oil, make sure your base coat has strengthening proteins and moisturizing vitamin E, says Dr. Jaliman. When it's time to remove your polish, ditch the acetone and grab a solution that doesn't contain this withering ingredient.OPI Acetone-Free polish remover, $6/4 fl. oz.; opi.com for salons.
Barielle Pro Nail Rebuilding Protein, $10; sallybeauty.com.Read MoreLess
Manicure Makeover: Secrets to Strong, Smooth Tips at Every Age