It is often a sign of a chemical deficiency in the body. 

Fingernails can reveal so much about your health and lifestyle. Nails are made from tough keratin protein, taking many different shapes.
Normal healthy fingernails curve gently, both from side to side and from finger to nail front edge.

Here is more information on finger nails.

http://www.indoindians.com/health/finger.htm

http://www.webmd.com/content/article/42/1689_50294.htm?lastselectedguid={5FE84E90-BC77-4056-A91C-9531713CA348

I hope this helps. Good luck and best wishes.