Surgical masks are ubiquitous in Japan, particularly during hay fever season. Image from Flickr user David Shackelford. License: Attribution-NonCommercial 2.0 Generic (CC BY-NC 2.0). Mild weather and beautiful cherry blossoms make spring arguably the best season in Japan. Many visitors to the country carefully time their trips to coincide with the blooming of the cherry trees dotted all across the country. However, some Japanese are less than eager to welcome the warmer weather. Instead, spring in Japan brings with it an invisible menace. Floating in the springtime air is a cloud of pollen grains that induce sneezing, sniffling, and itchy eyes and noses in hay fever sufferers all over the Japanese archipelago. When you think of springtime in Japan, the first thing that comes to mind is iconic clouds of cotton candy pink blossoms, known as sakura (桜) in Japanese. The flowers bloom earliest in Japan's southwest, advancing north- and eastward across the archipelago in what is known as the “cherry blossom front” or sakura zensen (桜前線). おはよーござまーす??早咲きの桜が満開だった！ pic.twitter.com/h9G9lbaGrc — きるしー@鞄鯖 (@kilcy_kilcy) 2017年3月28日 Good morning! The early flowering cherry blossoms are in full bloom! But the blossoms aren't the only thing making their way across Japan as the weather starts to warm up. Clouds of pollen also move from north to south, wreaking havoc on hay fever sufferers’ sinuses in the process. It isn't flowers that cause hay fever in Japan. The culprit is pollen from trees, in particular the Japanese cedar or sugi (杉, cryptomeria japonica) and Japanese cypress or hinoki (檜, chamaecyparis obtusa). A cedar tree releases clouds of allergy inducing pollen. Image from Flickr user Andy Heatwole. Image license: Attribution-NonCommercial-NoDerivs 2.0 Generic (CC BY-NC-ND 2.0). For western and eastern Japan (including Tokyo), hay fever season starts between late January and mid-February, as the weather begins to warm up. Cedar pollen production peaks in late March to early April and then steadily declines, while cypress pollination lags behind by about a month. Many Japanese netizens are taking to Twitter to document their symptoms. 花粉症がもろ出ちゃってつらい…? ティッシュがない時は鼻水垂れっぱなしだけど、それもファッションです。 — はやしん【レイターズ】? (@laters_hayashin) 2017年3月9日 My hay fever's acting up and I feel awful…! Whenever I'm caught without my tissues my nose runs constantly, but it's all part of my look. 今日だけでクシャミ６０回はしてます?? キタキタキターーーー花粉！！！ — 前田まみ(吉本新喜劇) (@mami_8224) 2017年3月9日 I must have sneezed about 60 times just today! It's heeeeeeere… the pollen!!! Japanese media tracks and reports on the pollen season each year in much the same way it reports on the blooming of the cherry blossoms. The map below shows the progression of the “cedar pollen front” or sugi kafun zensen (スギ花粉前線) across the country. その鼻水、風邪？花粉症？今年もあの季節がやってきた！２０１７年スギ花粉前線 https://t.co/3jr0Tjvahv pic.twitter.com/eWyyktddBP — まとめっツイ (@suvosuludov) February 8, 2017 Is your runny nose from a cold? Or is it from hay fever? It's that time of year again. Here's the “cedar pollen front.” The Japan Times reports an estimated one quarter of Japan’s population of 123 million people suffer from seasonal hay fever. But it hasn't always been this way. In fact, pollen allergies were rare in Japan until the 1960s. The rise of hay fever is closely linked to Japan’s forestation policy after World War II. As the nation rebuilt itself, demand for timber surged, and cedar and cypress were the trees of choice for the forestry industry. However, a wide availability of cheap, imported timber and the resulting decline of the Japanese forestry industry has meant that a lot of the trees that should have been cut down by now have been left to grow. Many of these trees are at least 50 years old—their peak pollen producing age. Cedar pollen. Image from Flickr user Tam Tam. Image license: Attribution-ShareAlike 2.0 Generic (CC BY-SA 2.0). While one might expect hay fever to be more common in rural areas with a lot of trees, in fact the opposite is true. In cities, pollen particles fall on concrete and asphalt rather than being absorbed by the soil. From there, they are swept up again by winds to recirculate. Japan's urbanization has also eliminated many of the farms and windbreaks that had once helped keep much of the pollen from reaching the city. Another contributing factor to Japan's hay fever problem is air pollution. In addition to exhaust gas emissions, PM2.5 pollution from China is an ongoing problem in Japan. Research shows that hay fever is exacerbated when pollen mixes with other pollutants in the air, another reason why the highest hay fever rates are found in cities, even though they typically have lower pollen counts than rural areas. Hay fever sufferers in Japan have no shortage of products to choose from.