Here are some clues about hair loss.
. With sudden hair loss that are all from the same patch or area the may be a loss of B vitamins from excess stress. Supporting with Biotics Research B vitamins occasionally stops the hair loss using the Bio B 100.
When the hair loss is occurring in a middle aged female there may be a thyroid gland imbalance. Check the Body Restoration book on this site for more information on thyroid gland imbalances as well.  When support is needed for a male, it may be due to an excess of a hormone called DHT that Apex Prosta DHT can support.
The other vitamins and supplements for hair loss include Flax Seed Oil, copper and calcium as well as zinc. A lack of Biotin may also cause Alopecia.
When this occurs in a teenager of younger, it may be due to the use of antibiotics (it can occur in adults too). This can be supported with good acidophilus and fermented foods.
The hair loss can skip a generation so look at the grandparents for a clue if this is the cause. Hormone imbalances and chronic infections may be the source as well.
If there are cold hands and feet, the problem could be due to poor circulation, same with poor nail growth. Look for anemia in these cases and protein deficiency and inositol. If the person takes too many pain killers this can do it too.