Do You Shed More in the Summer?

I have a somewhat wacky question about perimenopausal hair loss. Is there any research that suggests it is seasonal? I’m 46, and for the past two years, I’ve experienced it in spring and summer, and then it slows down in fall and stops in winter. Are there other hormonal shifts that would explain this phenomenon?

—Brenda

Your question is not wacky. In fact, you are on to something! There is evidence that there is seasonal variation in hair shedding, though this is not restricted to perimenopause. Hair follicles undergo a predictable cycle. Any individual strand may be in a different part of the cycle than its neighbors. At the end of the cycle, the strand will fall out. This is normal shedding. We are all shedding some hair all the time.

There are a number of studies looking for a seasonal pattern to this shedding by analyzing things like Google searches, but I think the most compelling one is a retrospective study in which researchers looked back at trichograms — these are microscopic examinations of plucked hairs — of more than 800 women over six years. They found that a greater number of hairs were in the telogen, or “resting,” phase in summer than at any other time of year. There is a second peak in spring. The telogen phase is also the time in the cycle when the hair eventually sheds, making way for a new strand. So what you are likely seeing is normal shedding that may be superimposed on perimenopausal hair loss.

In recent years, researchers have looked for possible reasons for the seasonal shedding that many women seem to experience. One theory is that there are seasonal rises and falls in our vitamin D levels. This makes sense. Our body synthesizes vitamin D in a process that involves exposure to sunlight. So vitamin D levels are lowest in about April (in the Northern Hemisphere) and highest in October.

Vitamin D has been found to play an important role in both hair growth and the hair cycle. Low vitamin D levels are associated with increased hair loss, which is why vitamin D supplements are often touted as a way to get thick, shiny hair (vitamin D is actually the main ingredient in Nutrafol). Unfortunately, there is no data to suggest that supplementing vitamin D reduces hair loss.

Ultimately, your observations that you lose more hair in the spring and summer is correct: there is data suggesting that the hair cycle is seasonal. The exact cause of this seasonality is not understood but may be related to seasonal fluctuations in vitamin D levels. However, supplementing vitamin D has not been shown to reduce hair shedding or loss.