A careful medical history and examination of the hair and scalp are usually enough to diagnose the nature of your hair loss.
Hair weaves, hair pieces, or changes of hair style may disguise hair loss. This is generally the least expensive and safest approach to hair loss. Hair pieces should not be sutured to the scalp because of the risk of scars and infection.
Diagnostic tests that may be performed (but are rarely needed) include:
Microscopic examination of a plucked hair
Skin biopsy (if skin changes are present)

Call your doctor if:
You are losing hair in an atypical pattern.
You are losing hair rapidly or at an early age (for example, teens or twenties).
You have any pain or itching associated with the hair loss.
The skin on your scalp under the involved area is red, scaly, or otherwise abnormal.
You have acne, facial hair, or menstrual irregularities.
You are a woman and have male pattern baldness.
You have bald spots on your beard or eyebrows.
You have been gaining weight or have muscle weakness, intolerance to cold temperatures, or fatigue.
Typical male pattern baldness involves a receding hairline and thinning around the crown with eventual bald spots. Ultimately, you may have only a horseshoe ring of hair around the sides. In addition to genes, male-pattern baldness seems to require the presence of the male hormone testosterone. Men who do not produce testosterone (because of genetic abnormalities or castration) do not develop this pattern of baldness.
Baldness is not usually caused by a disease, but is related to aging, heredity, and testosterone. In addition to the common male and female patterns from a combination of these factors, other possible causes of hair loss, especially if in an unusual pattern, include:
Hormonal changes (for example, thyroid disease, childbirth, or use of the birth control pill)
A serious illness (like a tumor of the ovary or adrenal glands) or fever
Medication such as cancer chemotherapy
Excessive shampooing and blow-drying
Emotional or physical stress
Nervous habits such as continual hair pulling or scalp rubbing
Burns or radiation therapy
Alopecia areata -- bald patches that develop on the scalp, beard, and, possibly, eyebrows. Eyelashes may fall out as well. This is thought to be an immune disorder.
Tinea capitis (ringworm of the scalp)
