Unseasonably warm Christmas triggers hay fever alert

The unseasonably mild weather over the past few weeks prompted experts from Wageningen University and Leiden University Medical Center to issue a hay fever warning for Christmas. According to these experts, with the temperatures well above 10 degrees, many hazel and alder trees will already be blooming by Christmas, leading to sneezing and watery eyes for those allergic to pollen, NU reports. The two species need a cold period in winter in order to bloom quickly when the temperatures rise. The light frost in mid October probably signaled the trees that it was winter and the higher temperatures now may cause them to bloom. The earliest blooming of a hazel tree was in January 2013, they generally bloom around February 15th.