Do you have trouble sleeping in the hot summer because the temperature doesn't drop even at night? Many people may find it difficult to fall asleep even after going to bed, or wake up quickly after falling asleep.

1. Two causes of insomnia in summer.

- Increased temperature in the bedroom.

In summer, the temperature and humidity are high, making the bedroom environment less than comfortable. This is because in addition to high temperatures, it is affected by radiant heat from walls and ceilings that warm up during the day. On top of that, it's humid and humid. If the temperature in your bedroom exceeds 28℃, the quality of your sleep will deteriorate and your internal body temperature will have a hard time dropping. This is why I have a hard time falling asleep even when I go to bed. Also, if your body temperature decreases less, your sleep will be shallower, making it easier to wake up in the middle of the night.

・Increased humidity in the bed.

Another cause of waking up in the middle of sleep is "back stuffiness." Normally, we sweat about one glass a night while we sleep, but in the summer, when temperatures are high, the amount of sweat we sweat can be more than double the normal amount. Sweat increases the humidity on your back against the mattress, and the relative humidity can reach 80-90 %. In an attempt to get rid of this unpleasant stuffiness on my back, I keep trying to find the cold parts of the sheets. The amount of tossing and turning will be 2 to 3 times more than in winter.

2. Frequent tossing and turning problems.

I'm trying to ventilate the dampness from my back that's stuffy from tossing and turning, but each time I do that, my sleep gets lighter. If your body is still for too long, you won't get deep sleep.

In addition to the frequency of tossing and turning, the time of day is also not good. This is a problem because I tend to toss and turn even during non-REM sleep. Rolling over usually occurs before and after REM sleep. REM sleep, which occurs every 70 to 110 minutes after falling asleep, is a state in which the brain is in shallow sleep and close to wakefulness. On the other hand, during non-REM sleep, the brain should be in a deep state of rest, but if you toss and turn a lot, you won't be able to sleep deeply and the temperature of your brain will drop less. Furthermore, the secretion of growth hormone, which helps in recovering from fatigue, is concentrated in the first half of sleep, non-REM sleep. This is probably why you tend to wake up feeling insufficiently refreshed.

3. What's the secret to getting through those hard nights?

- Reduce the humidity on your back with "hemp".

The secret to a good night's sleep in summer is to suppress the rise in humidity on the back. By using bed pads and sheets to keep your back refreshed, you will reduce unnecessary tossing and turning. The most suitable material is linen , which has excellent heat conduction and moisture absorption and release properties. Sarari, Sawayaka. It's a clichéd expression, but I can't find a better word to describe the feel of linen. Linen quickly dissipates body heat and dries out sweat. It is a highly functional fiber grown by nature.

・“Camel hair” that is comfortable throughout the seasons

It may come as a surprise, but camel hair is also a great material for summer. An experiment was conducted in an artificial climate room with a temperature of 29°C and a relative humidity of 70 %, which simulates a hot and humid summer bedroom.We found that with bedding made of camel wool, the humidity inside the bed was relatively low, keeping the bed comfortable. I was there. Psychological evaluations showed that camel hair felt less stuffy, and there were fewer requests to lower the room temperature. Camel wool is known for its warmth in the winter, but it has excellent moisture wicking properties and a high ability to regulate humidity, so it is considered functionally suitable as a bedding material in the Japanese summer.

・One-point advice

In summer, don't dry your futon until the evening. If you expose it to the setting sun for a long time, it will build up heat. We recommend drying for about an hour between noon and 2 p.m.

Related article: How to choose bedding and mattresses: Two basics.