Having visited Japan in July previously, I knew the weather would be extremely hot. Now that I've been here a few weeks…I can say that it is BRUTALLY hot. Here is a list of strategies–and warnings–for coping with the heat, and what worked for my family and me.
THINGS YOU MUST DO.
Cover your head. We absorb a huge amount of heat through our heads. Keep that in mind. I prefer a parasol (higasa in Japanese) over a hat, but anything is better than nothing. Now that I've been here a while, I never, ever go in the sun without my parasol and sunglasses. I'm a dude and IDGAF how it looks, and neither should you.
Drink lots of water. You will sweat, period. Force yourself to drink more water than you think is necessary. There are vending machines everywhere. And bathrooms are clean in Japan! Many train stations have them! Pro-tip: vending machines often have boxes where you can dispose of plastic bottles. Though there are few public trash cans anywhere, this is one useful exception. So don't worry about carrying around an empty bottle for too long. There's also an app called MyMizu where you can find sources for bottle refills. (There are also electrolyte drinks everywhere; I prefer Aquarius because Pocari Sweat tastes like Pedialyte to me.)
Listen to your body and don't overdo it. This heat is insane and, I'm sorry, but it will affect your ability to do stuff. You will need to take longer breaks and do less than you would in a milder climate. Consider starting off really early in the morning (like, if there is a shrine you want to see that opens at 6, go to the shrine literally at 6!), spending the hot afternoon at home in your hotel, then going out again around sundown. Or, plan on spending the hottest part of the day in a big museum; you can hide out in their cafe and write postcards or just read. Definitely consider whether, at 2:00pm with the sun beating down mercilessly, you want to be flitting in and out of thrift shops or waiting in line at Disneyland.
OTHER STRATEGIES.
I've already mentioned the water, protecting your head, and scheduling. Here are some other strategies I've seen. I tried them all except the neck ring. Read on…
Wear cool clothing. YMMV on what works for you. I went with very thin, light travel pants and synthetic shirts that were not too tight and not too baggy–the kind of clothing you buy from camping stores like REI. Thin Uniqlo Airism polos also work great for me (though I found that the Airism undershirts made me hotter, not cooler.) Shorts also work, or loose 3/4 pants. Some people feel that protection from the sun is more important than letting the skin "breathe" (because it's so dang humid here you'll sweat either way) so they wear long sleeves and pants or long dresses. What you don't want to do is wear your Levi jeans and a thick cotton t-shirt under a cotton polo. You'll sweat so much, and walk around wet and sticky all day. Synthetic, breathable fabric is your friend.
Wear sunscreen. Even though I'm literally never in direct sun because I use a parasol, the sun still gets me. I find I tolerate the heat better with suncreen. Every kombini sells an incredibly light, thin sunscreen lotion called Biore UV Aqua Rich. Put some on before you go out.
The face handkerchief. Small, square, washcloth-style handkerchiefs are ubiquitous in Japan, and for good reason. Wiping off your face and neck feels GOOD and cools you down!
The neck handkerchief aka cooling towel. There are long thin handkerchiefs you can wet and wrap around your neck. These provide some relief, too, but in the end I went with an open collar and just the face hankie. (H/t /u/DocChopper)
Battery-powered fans. You'll see these everywhere. If you get one, get a strong one. If you can find one that also creates mist, use that.
Hand fans. Old fashioned fans, either folding or paddle-shaped, have been in use for centuries because they work. I personally don't use one much. I prefer the face hankie, which you can also wet if you're desperate. But hand fans are good when you're in a castle or shrine or whatever and there's just no air moving.
The ice ring. These are little rings you put in the freezer and get down to 28°c then put around your neck. This is one I haven't used, because I heard they get warm after a while and then they are just clammy and gross, and you have to carry them around in your bag the rest of the day.
Avoid a backpack if possible. At first I used a backpack when I went out for the day. The problem is, that creates a sweat sink on your back and it's hot and gross. After a while I switched to a small cross-body bag that is just big enough for hand sanitizer, a notebook, maybe a bottle of water or tiny folding umbrella, wallet, phone, etc. and not much more.
Sunglasses. I've seen few Japanese people wear sunglasses. I don't care. For whatever reason they really help me cope with the heat.
WHAT ULTIMATELY WORKED FOR ME.
Everyone uses different strategies, but in the end, after much trial and error, I settled on the following elements as a routine that make me feel best equipped to handle the heat. From head to toe: higasa; sunglasses; sunscreen; drink lots and lots of water; light, synthetic clothing; carry a face handkerchief; and adjust my schedule.
I would love to hear what worked for others, and what have I missed?
Have fun and stay safe everyone!
EDIT: OMG how could I forget the other interesting cooling gadgetry on offer here. The first two of these are very common:
Cooling spray This is a spray that's kind of like ICY-HOT in a bottle that you spray on the outside of your clothes. Some people swear by this, but for me some got on my skin and made it burn
Cooling wipes Disposable wet wipes with a sort of minty cooling solution in them. I personally prefer a wet wipe or wet towel.
Fan jacket These jackets, which have a fan built in that inflates the jacket and circulates air inside, might seem comical when you first see them. But after being here a while, you'll realize: if it works to cool you down, rock and roll baby.
by Caliquake