What causes high levels of tree pollen?

I ask because Southern California has been experiencing high levels lately, but this seems odd to me since it is the middle of winter.



  1. 0 Votes

    Tree pollen can be a problem even as early as January—namely birch trees, hazel, elm, alder and yew—and can travel far distances, especially if it has been dry out.  The trees that release pollen later in the season and in the summer are different from the ones right now.

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