It could be a variety of things. I found this quote online
Quote:
Hair loss can be triggered by a variety of factors including pregnancy, stress, surgery and age-related hormonal changes, to name a few. But few people realize that weight loss can also cause hair to shed, likely due to a nutritional deficiency. Although iron deficiency is often associated with diet-related hair loss, a range of nutrient deficiencies can result in thinning hair, dermatologists say. Changes in levels of zinc, magnesium, protein, essential fatty acids and vitamins D, B and A can all trigger episodes of shedding hair. The problem affects both men and women, but women are more likely to notice it and seek treatment, say doctors.
The full article is at
http://www.post-gazette.com/pg/05256/570686.stm and contains a lot of interesting information.