Hair loss (alopecia) is defined as losing enough hair that a person has visibly thin or balding patches. In order to diagnose hair loss, a physician will obtain the patient’s complete medical history, including recent or past illnesses and current medications, and review any family history of hair loss. Patients may also be questioned about their diet and hair care habits (e.g., dying, blow drying). Female patients may also be asked about menstrual cycles, pregnancy history and menopause. In addition, the physician will perform a physical examination, during which he or she will observe the total amount of hair on the scalp and analyze how it is distributed.

Men with androgenetic alopecia (pattern hair loss) usually lose hair on the crown of the scalp and around the temples, making diagnosis relatively routine. Women with androgenetic alopecia usually lose hair on the crown, starting with a widening of the part of the hair. 

Additional testing may be performed (e.g., skin biopsy) to check if other hair conditions (e.g., alopecia areata, telogen effluvium) or certain illnesses that cause hair loss may be responsible or occurring in conjunction with hair loss. Skin infections that may cause hair loss (e.g., ringworm) can be diagnosed by examining skin samples from the scalp. Examining pulled hair for differences in thickness and length may also help confirm a diagnosis.

In cases of severe hair loss with signs of accompanying illness, a variety of blood tests or imaging tests may be used to determine if an underlying condition or disease is responsible or occurring in conjunction with hereditary hair loss. Numerous medications have side effects that may cause hair loss, including anticoagulants (decrease blood clots), anticonvulsants (treat seizures), beta blockers (lower blood pressure) and antidepressants (treat depression).

Charts depicting different types of hair loss information may be used in some cases. However, they are insufficient to diagnose what may be responsible. The Hamilton-Norwood classification chart breaks down the progression of male pattern hair loss into seven classes. Initial hair loss (stages 1 and 2) typically consists of a receding frontal hairline. This recession becomes more defined over the temples and crown area of the scalp in the intermediate period (stages 3 through 5). Finally, total hair loss over the top and upper sides and back of the scalp characterizes the most advanced progression of the condition (stages 6 and 7). Modified versions of the system may be used for patients with different balding patterns.

The Ludwig classification system may also be used to describe levels of female pattern hair loss. The Ludwig system organizes levels of hair loss in the following manner:

• Grade I. Minimal widening of the hair part.
  
• Grade II. Moderate thinning or widening of the part.
  
• Grade III. Extensive thinning and widening of the part.