The most important cause of baldness is Male/Female Androgenic Alopecia, affecting almost 50% of adult males and 25% of adult women. You can see more about this here: male pattern baldness and female pattern baldness.
This cause of hair loss is directly related to levels of DHT, or Dihydrotestosterone, which is a sex steroid and androgen hormone and causes 95% of all hair loss. DHT miniaturizes hair follicles by shortening the anagen (growth) phase and/or lengthening the telogen (resting) phase – see more about hair growing cycles. Under the influence of this factors the hair follicles become progressively smaller and eventually disappear – this process is called “miniaturization.” So, it’s your hormones and it’s your genes contributing to you loosing of hair! Slowly, your hair follicles are getting progressively sensitive to your own hormones.
For this reason, once increased hair loss occurs the first measures for healthy hair re-growth is one of two things: DHT inhibiting to decrease it’s level from your body, OR hair growth stimulation even in DHT’s presence. This tasks can only be achieved by using special products and medication, backed by extensive scientific research. And because men is from Mars and women is from Venus :), you guys look in the Men’s Guide for Hair Loss Treatment, and you gals go for the Lady’s Guide for Hair Loss Treatment.