About 1/3 of adults will have hair loss starting anywhere between the teens and the 40's. Men tend to get the M-shaped pattern above the forehead, while women's hair is more likely to become thinner all over the head. While it's not possible to reverse the hair loss process, there are many ways to style hair, get extensions/wear a wig, or just embrace your new look. For those wanting to slow or stop balding, there are multiple remedies on the market. However, the only proven treatments are medicated shampoo (Rogaine) and oral prescription medication (finasteride aka Propecia for men, and spironolactone for women).
For more information, please read my interview on CNNHealth with Dr. Jeffrey Benabio of The Derm Blog