Summer isn't only about being hot.
While everyone around you is groaning "so hot," you sometimes feel oddly chilly. The forecast said 30 degrees, but it's actually 28. You're walking and you feel a bit cold. By any logic you should be sweating, yet your body, which I like to call "Body-kun," like a game character I'm stuck controlling, reports "currently cooling down."
Then you go to bed and wake up itching. You look, and there's a swollen bump that looks exactly like a mosquito bite. Is the culprit still in the room? I've been seeing a lot of mosquitoes outside lately, too. Ugh. And then I spotted it. It was there.
Summer discomfort isn't a big event. But small glitches and small enemies like these quietly chip away at your sleep and your daily HP (your energy bar).
You can feel cold even at 28°C
On paper, 28°C is plain old hot.
But how warm or cold you feel doesn't depend on air temperature alone. At the very least, these things all mix in:
- Whether wind is hitting you
- Whether you're sweating
- Sun or shade
- How humid it is
- Whether your clothes are soaked with sweat
- Whether you're walking or standing still
- Whether you're hungry, sleep-deprived or tired
The biggest ones are sweat and wind.
When sweat evaporates off your skin, it carries heat away from your body. That's exactly how your body is meant to cool down. Sweating is how it lets heat out.[^sweat]
Add wind, and even more heat leaves the surface of your skin. You walk a bit and get slightly sweaty. Then a gust funnels between buildings, or comes off the river, or blows through the shade, or slips under your shirt. Even at 28°C, your skin's sensors can decide "this is cold."
So if everyone else is hot and you're chilly, it doesn't necessarily mean something is wrong with you.
It may simply be that you happen to have all the cooling conditions lined up.
"Cold on a hot day" is just a surface-cooling log
What matters here is telling apart two cases: your whole body is actually cold, or only your skin is.
If the following sounds like you, it's probably down to the environment:
- You'd been walking
- You were lightly sweating
- You were somewhere the wind blows through
- You were in the shade
- You were in short sleeves or thin clothes
- Wind was hitting your neck, arms or back
- The chill disappeared once you left the spot
In that case, your body is basically just reporting "my outer layer got cooled."
On the other hand, if you notice the following again and again, treat it as a separate matter:
- You feel cold even with no wind
- Only your hands and feet are unusually cold
- You have shivering, dizziness or heavy fatigue
- You get out of breath easily
- You've become someone who is always cold
- You've had weight changes or strong exhaustion
If those keep up, it may be worth getting checked for things like anemia, thyroid problems, blood sugar or fatigue.
But in a case like this one, with 28°C, walking, and a spot that sounds like a wind tunnel, I'd say it's quite likely evaporative cooling from wind plus sweat.
How soon does a mosquito bite swell up?
You wake up itching.
You look, and there's a puffy bump like a mosquito bite.
With mosquitoes, that swelling shows up fast. A mosquito bite has an immediate reaction that appears within minutes of the bite, forming a round raised welt that peaks at around 20 to 30 minutes.[^mosquito-reaction]
So if you were bitten in your sleep, it's perfectly normal for the bump to be there by the time you wake up.
Roughly, it goes like this:
- Right after the bite to a few minutes: itching, redness, a puffy bump
- Around 20 to 30 minutes: swelling and redness are most noticeable
- A few hours to the next day: it can turn into firm, itchy bumps
- 1 to 2 days later: itching lingers, and scratching makes it last longer
So "I woke up and it was swollen" is very much what a mosquito does.
Of course, bed mites, fleas, bed bugs and hives can look similar. But one bump, on exposed skin, puffy, itchy, and a mosquito in the room? With all of that lined up, the suspect list gets very short.
Is it still in the room?
It might be.
A mosquito doesn't vanish into another dimension right after biting you. It can rest on a wall, the ceiling, a curtain, behind furniture, in a dark corner, or near your bed.
What makes a mosquito at night so exhausting isn't the bite itself. It's that an enemy you can't confirm is there holds your sleep hostage.
You hear the whine. You itch. You wake up. You turn on the light. You check the walls. Nothing. You lie down. You feel like it's still there.
That loop is the worst.
And this time, it was really there in the end.
So it wasn't in my head. A hostile presence had been confirmed in the room.
When do mosquitoes show up in Japan?
The common "yabuka" (the striped tiger mosquitoes you meet outdoors), especially the Asian tiger mosquito (Aedes albopictus), is said to be active in Japan from roughly mid-May to late October. Japan's Ministry of Health, Labour and Welfare says in its Q&A that this species is highly active outdoors during the day, with a range of about 50 to 100 meters, and that its season in Japan is generally from mid-May to late October.[^mhlw-dengue]
So seeing lots of mosquitoes outside in July isn't strange. It's just peak season.
If it feels like they suddenly multiplied over the past few days, this sequence is possible:
- It rains
- Water stays in plant saucers, drains, gutters, buckets, empty cans and so on
- Mosquito larvae grow
- A few days to a couple of weeks later, adults increase
- You think, "wait, why are there so many mosquitoes lately?"
Summer mosquitoes don't so much appear out of nowhere as show up in your daily life a few days after the puddles.
Tonight, the best move is to build your defenses, not hunt
When you see a mosquito, you want to kill it.
Fair enough.
But if you go into full search-and-destroy mode right before bed, your brain wakes up. Walls, ceiling, curtains, behind the furniture, under the bed, the closet, everything starts to bug you. The fight was supposed to protect your sleep, and the fight itself ends up eating it.
So just for tonight, here's the order of priorities:
- Turn on the light
- Check the walls, ceiling, curtains and around the bed
- If you find it, kill it
- If you don't, use a push-type spray or an electric mosquito repellent as the instructions say
- Use a fan to create airflow around your body
- Cool the bitten spot
- Don't scratch, and go to sleep
A fan is strong as a defense because it also makes it harder for mosquitoes to fly. It won't shoot them all down, but it can put a wall of wind around you while you sleep.
Still, remember the earlier "28°C but chilly" problem. Blast yourself with wind and your body will get cold. Rather than aiming it straight at you, create a gentle flow of air around your bed.
Not scratching is the hardest part
Dealing with a mosquito bite is easy to put into words.
- Cool it
- Don't scratch
- Use anti-itch medicine
- Don't crush it with your fingernails
- Watch out if redness or heat spreads
But in practice, "don't scratch" is the hardest part.
Itching is a very loud notification from your body. And at night, with little else going on, the itch alert sits in the center of the screen the whole time.
Scratching feels good for a second. But it irritates the skin and makes the itch worse. Body-kun sends another "emergency event" alert.
So before bed, use physics rather than reason.
Cool it. Put medicine on. Take your hand away. Get under the covers.
Don't try to win with willpower.
Summer fatigue is worn down by small interruptions, not big problems
The heat itself is draining in summer.
But what really chips away at your daily HP is often a string of small interruptions like these:
- It's 28°C but you feel chilly
- Wind cools you down
- Sweat makes your clothes uncomfortable
- You try to sleep and there's a mosquito
- You get bitten and it itches
- You wonder whether the culprit is still in the room
- You wake up fully while searching for it
- You end up short on sleep
- You're tired the next day
Each one is small.
But summer life is full of small bugs like these.
Hot yet cold. Sleepy yet itchy. Want to sleep but there's an enemy.
I think this is Body-kun's processing load going up.
Conclusion: not in your head, just the environment and an enemy teaming up
Summing up this episode, it's pretty straightforward.
Feeling chilly at 28°C was probably surface cooling from sweat and a windy spot.
Waking up itchy is a natural immediate reaction to a mosquito bite.
A mosquito bump can appear within minutes and is most noticeable at 20 to 30 minutes.
Seeing lots of mosquitoes outside in July is normal peak season.
I wondered if one might still be in the room, and it really was.
So it wasn't in my head.
In summer, Body-kun is made to handle heat, chills, itching and sleep disruption all at once.
That's why feeling worn out is normal.
Tonight's best move isn't digging too deep into causes. It's dealing with the enemy in the room, adjusting the airflow, cooling the itch, and going to sleep.
The win condition in summer isn't staying comfortable.
It's not letting a small enemy steal your sleep.
Related link ideas
- Body-kun log: telling apart "cold on a hot day"
- What wrecks your sleep may be small interruptions rather than big events
- Beating summer discomfort: look at perceived temperature, not air temperature
- Itching, noise and notifications: the small enemies that wake your brain at night
References
[^sweat]: Taisho Kenko Navi, "What is sweat? Let's sweat properly for our bodies!" https://www.taisho-kenko.com/column/133/ [^mosquito-reaction]: Vander Does A, et al. “Update on mosquito bite reaction: Itch and hypersensitivity, pathophysiology, prevention, and treatment.” https://pmc.ncbi.nlm.nih.gov/articles/PMC9532860/ [^mhlw-dengue]: Japan's Ministry of Health, Labour and Welfare, "Q&A on dengue fever" https://www.mhlw.go.jp/bunya/kenkou/kekkaku-kansenshou19/dengue_fever_qa.html [^mhlw-prevention]: Japan's Ministry of Health, Labour and Welfare, "Request for cooperation on mosquito control under the national summer mosquito-control campaign" https://www.mhlw.go.jp/stf/houdou/0000126086.html
