If you’re travelling to Tokyo during the summer months note that it can get very hot. The so-called heat island effect is a major factor, caused by a combination of the sun’s rays reflected off the asphalt, and the heat exhaust from air conditioning. So make sure you drink plenty of fluids so you don’t get dehydrated, wear protective clothing, and try and stay in the shade.
One bothersome aspect of life in Tokyo is the high pollen count, particularly from the cedar and cypress trees which grow in the region. You will see people wearing masks on the streets of Tokyo to block the pollen. The hay fever season starts in February, so if you’re a hay fever sufferer planning to travel in the spring you should definitely see a doctor and stock up on appropriate medication before you leave for Japan.