Renee Zellweger has been at the top of the celebrity hair loss discussion for some time. The main reason for this may simply be because she happens to have hair that is somewhat thin. However, another reason for the rumors about her being an actress with thinning hair stems from rapid weight gain and weight loss when she was filming the Bridget Jones movies.
Sudden weight loss such as that experienced by Zellweger can lead to Telogen Effluvium (TE), a type of hair loss. This happens when a person sheds more hair due to severe or sudden stress, extreme diet, surgery or any other traumatic event in life. During this time of stress the hair follicles may enter into the Telogen or resting phase and cause hair shedding. Often times the person may have already recovered from the stressful event by the time the hair loss occurs.
Some of the factors that may cause TE include being involved in an accident, taking certain medications, sudden weight loss, childbirth, and severe emotional distress. While this type of hair loss is typically temporary, if Renee continues this yo-yo dieting she is increasing her risk of developing Telogen Effluvium.