The weather...

Not a stupid question at all.

Virtually all of us have periodic shedding of hair to some degree at different times during the year. This shedding is usually at a maximum at the end of summer and the beginning of autumn. Like the rest of the animal kingdom, humans are affected by summer and winter climatic changes.

In animals, there is a clear season of hair growth, shedding and replacement with a summer or winter coat. For humans it is the same. Our hair growth and shedding changes with the seasons. It is theorized our bodies determine the number of sunshine hours we receive and this dictates hormone production which, in turn, affects hair growth and shedding. The pineal gland and changes in melatonin levels seem to be the most important in this seasonal shedding of hair.

Hope this answers your question. ;)