Telogen effluvium is the second most common cause of hair loss  due to an increased number of hair follicles entering the resting stage.It is most commonly caused by stress whether its death, pregnancy, illness, weightloss. The most common causes of Telogen Effluvium are:

Health Conditions

There are some health conditions which may go undetected that can contribute to hair loss. These include anemia or low blood count and thyroid abnormalities. Both of these conditions can be detected by a simple, inexpensive blood test. Once reversed you will notice hair regrowth.

Diet Considerations

Hair loss may also occur due to dietingHowever, the vitamins cannot prevent hair loss associated with rapid, significant weight loss. Furthermore, many of these supplements are high in vitamin A which can magnify the hair loss.

Physical Stress & Emotional Stress

Surgeries, severe illnesses and emotional stress can cause hair loss. The body simply shuts down production of hair during periods of stress since it is not necessary for survival and instead devotes its energies toward repairing vital body structures. There can be a three month delay between the actual event and the onset of hair loss. Furthermore, there may be another three month delay prior to the return of noticeable hair re-growth. This then means that the total hair loss and re-growth cycle can last 6 months or possibly longer when induced by physical or emotional stress. When the above causes of telogen effluvium are reversed or altered you should see the return of normal hair growth.

Medications:

Ace inhibitors, (Blood pressure medications)
Antiarthritic drugs: Naproxen, Methotrexate
Anti Cancer Drugs
Anti Coagulant Drugs: Heparin Warferin
Gout Medication
Anti depressants
Thyroid Medication
Parkinsonian medication
High doses of Vitamin A