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Sleep is an incredibly complex process that affects virtually all systems of the body. It serves an essential biological function, and it is fundamental to well-being. Without enough rest, you may see short-term health problems such as impaired memory and lack of alertness. If you experience too much sleep deprivation, you may start seeing long-term and serious health problems, including high blood pressure, diabetes, or depression. That is why getting a good night’s sleep should be your priority.

There are many steps you can take to improve your sleep quality. These include maintaining a well-balanced diet, exercising regularly, and clearing your mind before going to bed. Perhaps the most important thing to do is to make sure that you’re in the human comfort zone before sleeping.

What is the human comfort zone for temperature and humidity?

The human comfort zone (also known as human thermal comfort) refers to a condition of mind that expresses satisfaction with its surroundings. Generally, people experience thermal comfort when staying in environments with temperatures between 22 °C–27 °C and relative humidity of 40%–60%.

Staying in places with high levels of temperature and humidity makes people feel discomfort and sometimes heat stress—a condition that reduces the body’s ability to cool itself. Without thermal comfort, falling asleep can feel like an arduous process.

The Role Relative Humidity Plays in Sleep

Humidity is the level of moisture content in the atmosphere. Meanwhile, relative humidity refers to the ratio of the maximum amount of water vapour that the air can hold at a given temperature to the actual amount of water vapour in the air. At the threshold between 40% and 60%, relative humidity does not leave a major impact on thermal comfort. As such, maintaining the relative humidity in your room within this range should be a priority.

How Your Body Reacts to High Relative Humidity

Humans, by nature, are very sensitive to humidity. This is because our skin relies on the air to get rid of moisture when we perspire. Your body’s primary method of regulating temperature is the process of perspiration. When sweat evaporates off of your skin, your core body temperature cools down, bringing you a feeling of relief. However, if there is too much moisture in the air because of high relative humidity, sweat will not evaporate. This leads to discomfort, as we feel much hotter than the actual room temperature.

If you’re exposed to high relative humidity for too long, sweat will accumulate and your clothes may get drenched, making you feel too uncomfortable to sleep peacefully. With too much moisture in the air, falling or staying asleep becomes far more difficult. This also affects the time you spend in certain sleep stages. Aside from exacerbating nighttime sweating, high relative humidity also increases wakefulness and reduces the time you spend in sleep stages, which are crucial for your overall health.

Humidity also affects sleep in indirect ways. If left unchecked, excessively damp rooms will turn into breeding grounds for mould, dust mites, and other allergens that thrive in humid environments. People who sleep in these rooms may experience increased allergy or asthma symptoms.

The Effects of Exposure to Low Relative Humidity

Low relative humidity can make our sweat evaporate easily, allowing us to feel much cooler than the room temperature. However, extremely low humidity can also cause dehydration, especially in the winter and fall. To make matters worse, most home heating systems produce dry heat, which consumes what little moisture is left in your indoor air.

At extremely low humidity, you are exposed to dry air, which can irritate your throat and sinuses. This can cause you to wake up parched or sleep uncomfortably due to chronic irritation or infection. Air with little to no moisture can also lead to dry skin, dermatitis, nosebleeds, eye irritation, and health problems.

How Temperature Affects Your Sleep

No one is a stranger to the struggle of falling asleep when temperatures start to dip too low in winter or rise too high in summer. It is particularly difficult to enjoy a peaceful slumber when you’re overheating during a summer heatwave. Waking up with cold feet during winter will also put a damper on your day.

There are many reasons why you would be tossing and turning at night, but one cause you might overlook is your bedroom’s ambient temperature. Even the smallest changes in ambient temperature can negatively or positively affect your sleep quality.

Our sleeping patterns rely heavily on circadian rhythms, which are internal biological processes designed to regulate our bodies over a 24-hour period. Your circadian rhythm lets your body know when it's time to wake up or fall asleep. Typically, our circadian rhythms align with the rise and fall of the sun. As a result, light and temperature play large roles in preparing our bodies for sleep.

The Science Behind Sleeping

The circadian rhythm is our internal “body clock” that regulates the sleep cycle. This body clock controls when you feel tired and ready for bed or refreshed and alert. After waking up, you’ll increasingly feel tired throughout the day. The level of tiredness you feel will peak in the evening leading up to your bedtime.

Our circadian rhythms are regulated by the suprachiasmatic nuclei (SCN), which are located in the middle of the brain. SCNs are connected to different parts of the brain and act as the control centres for circadian rhythms and other body functions.

One of the main functions of your body clock is to respond to light cues. It is also responsible for ramping up the production of melatonin, the hormone associated with the sleep-wake cycle, at night. When our body clock senses light, the production of melatonin starts to die down.

Light seems to play the largest role when it comes to setting your body clock. Because sunlight and other time cues affect the circadian rhythm, blind people often have problems with their sleep.

Understanding the Sleep Cycles

Over the course of the night, your brain goes repeatedly through two different cycles of sleep. These are REM (rapid-eye movement) and non-REM sleep. Throughout your slumber, you will go through four to six rounds of these sleep cycles, not all of which will last the same duration. On average, each round of the sleep cycle will last around 90 minutes. The first part of the sleep cycle is non-REM sleep, which can be divided into the following:

First Stage

The first stage marks the line between being awake and falling asleep. It is also known as the stage where you start to doze off and usually lasts between one to five minutes. During this stage, your body hasn’t fully relaxed, but the bodily functions and brain activities start to slow down with periods of brief movements. Waking people up at this stage is often easy, but if they are left undisturbed, they can quickly transition into the second stage of non-REM sleep.

Second Stage

The second stage is known as light sleep. During this stage, your heart rate and breathing are regulated and your body temperature starts to drop. At the same time, eye movement stops and brain waves show a new pattern. Generally, most of your brain activity slows down at this point. However, short bursts of brain activity will occur from time to time, which helps in resisting being woken up by external stimuli.

Depending on a person’s age and habit, this stage of sleep can last between 10-25 minutes during the first sleep cycle. Each second stage sleep can become longer throughout the night. Typically, half of the time you spend sleeping will be in this stage.

Third Stage

The third stage is also known as deep sleep. During this stage, waking people up becomes significantly more difficult. Your pulse, breathing rate, and muscle tone decrease during these stages as the body relaxes even further.

Studies suggest that this stage play a critical role in restorative sleep, which promotes bodily recovery and growth. Aside from its role in tissue restoration, deep sleep also helps in shoring up the body’s immune functions and assists in processing memories. While there is a significant drop in brain activity at this stage, studies suggest that deep sleep promotes insightful thinking, contributes to creativity, and bolsters memory.

During the first half of the night, we spend the most time in deep sleep. These stages commonly last for 20-40 minutes during the early sleep cycles. As the night unfolds, deep sleep stages get shorter, as we transition into spending more time in REM sleep instead.

The REM Stage of Sleep

As you cycle into the REM stage of sleep, your eyes move rapidly under your closed lids and your brain waves become similar to what you exhibit during wakefulness. Most of your dreaming takes place during this stage. While you are in REM sleep, your muscles become temporarily paralyzed to prevent you from acting out your dreams or putting yourself in danger.

REM sleep involves more brain activity than NREM. It is considered to be a more wakeful state, since your heart rate and blood pressure increase to levels close to what you experience when you are not asleep.

This stage of sleep helps your brain consolidate and process new information. Your brain then retains this information in your long-term memory. REM sleep also helps in ensuring better mood regulation and mental concentration.

Improving Your Sleep Quality

Enjoying a peaceful slumber when you're in an uncomfortable environment can be difficult—it can even be downright impossible. Staying in a damp, cold room or one that is excessively dry and hot can interfere with your sleep. If it takes hours for you to drift off or your slumber gets interrupted several times in the middle of the night, it’s time for you to take action. There are many ways to improve your sleep quality including the following:

Creating the Perfect Bedroom Environment

Sometimes, even the smallest changes to your bedroom environment can leave a huge impact on the quality of your sleep. Optimize your bedroom to ensure the ideal conditions. Make sure your room is at the perfect temperature and manage its relative humidity.

Maintaining a Healthy Bedtime Routine

Sticking to a bedtime routine sends a powerful signal to your brain, letting it know that it’s time to wind down and go to sleep. Try your best to stay in sync with your body’s natural sleep-wake cycle or circadian rhythm. Maintaining a regular bedtime schedule enables you to wake up feeling more refreshed and energized.

Managing Light in Your Room

When you are in a dark environment, your brain ramps up the production of melatonin, which is the hormone responsible for making you feel drowsy. By controlling the amount of light present in your room, you can influence the production of this hormone, thus helping you manage your sleep cycle.

Clearing Your Mind

Your mental state directly affects your ability to sleep comfortably. As you let residual stress, worry, and anger linger in your mind, falling asleep becomes a more difficult task. That is why you should take steps to manage your emotions and overall stress levels. Curb the worry habit so that you can unwind at night with ease. One way you can do this is by developing a relaxing routine. Prepare your mind for sleep by taking a warm bath, drinking a warm glass of milk, or listening to soft music and turning off the lights. If you are not used to sleeping in a pitch black room, you can use a night light.

Staying in the Human Comfort Zone

By staying in temperatures between 22 °C–27 °C and relative humidity of 40%–60%, your body experiences thermal comfort. As a result, falling asleep becomes an easier task. There are many ways to stay within the human comfort zone. These include managing your thermostat, using electric blankets, installing a humidifier (or a dehumidifier, depending on the relative humidity of your room). You can also stay warm and comfortable by taking advantage of electric blankets, heating cushions and foot warmers.