• Eat a high-protein diet, including Brewer’s yeast, calcium, silica, and, if necessary, hydrochloric acid.

• Water causes the nails to swell and they shrink when dry, resulting in loose, brittle nails.

• Avoid immersing the hands in detergent water.

• Never cut the cuticles. This damages the nail and invites infections. Do not push them back.

• Brittle nails are common among teenagers, pregnant women, and those with food allergies. The problem is malabsorption or nutritional deficiencies (unsaturated essential fatty acids, amino acids, calcium, iron, or zinc).

• Hangnails are caused by an essential fatty acid deficiency. Put vitamin E oil or aloe vera directly on it, to reduce further breaking and likelihood of infection. They are particularly common among women who have their hands in water a lot or who bite their nails. Keep nails clipped short. Rub vegetable oil into the hands occasionally.

• If you tend to pick at your nails, wear clothes with pockets; and, when you find yourself starting to do it, put your hands in your pockets.
References :
http://www.pathlights.com/nr_encyclopedia/frames03.htm