When dealing with hair loss
, the first thing is to determine if the hair loss is occur just in one or a few places or all over. If the loss is mostly just in a few places, then focal causes are more likely, such as trauma (for example, the tugging on the hair shafts by a pony tail can do this), tinea capitis (fungal infection of the scalp) or alopecia areata (an autoimmune condition which tends to cause hair loss in scattered circular areas on the scalp).
On the other hand, if the hair loss is more diffuse all over the scalp then other things are possible. Generally, medical causes such as thyroid disease or iron deficiency need to be ruled out. Additionally, if the hair loss is more on the temple and forehead hairline, this could be a pattern baldness and it may be related to a hormone imbalance, which could be detected with certain blood tests. If, on the other hand, the hair loss is more diffuse and can be correlated to a recent illness, new medication, or stress, then this is likely to be telogen effluvium, which is a temporary and self correcting hair loss.
Start by talking to your primary care doctor