Why do I lose a lot of hair each fall?

Ask the doctors

Q. I have fairly thick hair in the summer, but it seems to thin out in late fall. Is there anything I can do now to prevent losing hair in a few months?

A. Sadly, no. What you've experienced is common to all of us. On average, about 90% of the hairs on our heads are in the growing phase and about 10% are in the resting phase. After a few months in the resting phase, the hairs are shed. It's normal to shed up to 100 hairs a day.

A 2011 study by Swiss researchers determined that the growing/resting cycle isn't uniform throughout the year but has seasonal peaks. The researchers evaluated the hair growth patterns of 823 women over six years. They found that more hair entered the resting phase in the summer — and was shed during the fall — than at any other time of year. No one has determined why this is so or how to disrupt the cycle. However, you can be reassured that seasonal shedding isn't the onset of permanent hair loss and that your hair will be at its fullest again next summer.

— by Hope Ricciotti, M.D., and Hye-Chun Hur, M.D., M.P.H.
Editors in Chief, Harvard Women's Health Watch