The symptom of both acute and chronic telogen effluvium is increased hair shedding. Patients usually only complain that their hair is falling out at an increased rate. Occasionally, they note that the remaining hair feels less dense. In both forms of telogen effluvium, hair is lost diffusely from the entire scalp. Complete alopecia is not seen.
Acute telogen effluvium is defined as hair shedding lasting less than 6 months. Patients with acute telogen effluvium usually complain of relatively sudden onset of hair loss. Careful questioning usually reveals a metabolic or physiologic stress 1-6 months before the start of the hair shedding. Physiologic stresses that can induce telogen effluvium include febrile illness, major injury, change in diet, pregnancy and delivery, and starting a new medication. Immunizations also have been reported to cause acute hair shedding. Papulosquamous diseases of the scalp, such as psoriasis and seborrheic dermatitis, can produce telogen effluvium.
Chronic telogen effluvium is hair shedding lasting longer than 6 months. The onset is often insidious, and it can be difficult to identify an inciting event. Because of the duration of the hair shedding, patients are more likely to complain of decreased scalp hair density, or they may note that their hair appears thin and lifeless.
The physical examination is the same in both acute and chronic telogen effluvium. Physical findings are sparse. Usually, the physician does not appreciate a decrease in hair density. However, if the patient’s hair has been falling out for several months, the hair may appear thin when compared with old photographs.
Physiologic stress is the cause of telogen effluvium. These inciting factors can be organized into several categories, noted below. Evidence from mouse studies indicates that psychological stress can induce catagen, mainly by effects on neurotransmitters and hormones.  In humans, however, the role these effects play in hair loss has not yet been determined. While substance P has been extensively studies in human hair follicles in vitro, in vivo studies have not been performed.  In HIV disease,  apoptosis may be related to HIV-1 viral protein R.  Note the following causes:
Acute illness such as febrile illness, severe infection, major surgery, and severe trauma
Chronic illness such as malignancy, particularly lymphoproliferative malignancy; and any chronic debilitating illness, such as systemic lupus erythematosus,end-stage renal disease, or liver disease
Hormonal changes such as pregnancy and delivery (can affect both mother and child), hypothyroidism, and discontinuation of estrogen-containing medications
Changes in diet like crash dieting, anorexia, low protein intake, and chronic iron deficiency: A study by Olsen et al sought to determine if iron deficiency played a role in female pattern hair loss. Results indicated that iron deficiency is common in women but is not significantly increased in patients with female patterns of hair loss or chronic telogen effluvium when compared with control subjects.
Heavy metals such as selenium, arsenic, and thallium
Medications, of which the most frequency cited are beta-blockers, anticoagulants, retinoids (including excess vitamin A), propylthiouracil (induces hypothyroidism), carbamazepine, and immunizationsAllergic contact dermatitis of the scalp