The leading cause of hair loss is androgenetic alopecia, also known as male pattern balding. Other reasons, however, can be lifestyle-related, such as smoking, poor diet, and stress. In addition, medical conditions and medication can also cause thinning hair. Unfortunately, alopecia is permanent. If it's another reason that's causing damage or miniaturization to the hair follicle, this can be slowed or fixed with proactive measures. As long as the follicle is intact, there is hope of reviving it; however, if it is damaged, scarred, or has disappeared, you won't have any success.