Biotin. Biotin is an oral supplement that helps strengthen skin, hair and nails. Usually a vitamin store can help you with proper dosage.
First.... ..Make sure there is no underlying internal cause, such as an under- or over-active thyroid. Then, keep your hands away from soap and water and harsh chemicals as much as possible. Take biotin (one of the b vitamins), about 5000 units per day. Eat a healthy diet. That's about as natural as it gets.