Many people notice that their hygrometer shows a higher reading in the morning than the night before. This is no coincidence: there are a few simple, explainable reasons why humidity increases while you sleep.
Your body produces moisture while sleeping
A sleeping person loses several hundred milliliters of moisture per night on average through breathing and skin. With two people in a bedroom, that can quickly add up to half a liter or more. In a closed bedroom with the doors and windows shut, this humid air has nowhere to escape, and the humidity gradually rises throughout the night.
Less ventilation during the night
During the day, doors are opened and closed more often, you walk around the house, and you sometimes ventilate more unconsciously. At night, the bedroom remains closed for warmth and quiet, meaning there is little air circulation. The moisture your body releases therefore largely stays in the room.
Temperature drop also plays a role
At night, the temperature often drops slightly, especially if the heating is set lower or turned off. Colder air can hold less water vapor per cubic meter than warm air. The same amount of moisture therefore results in a higher relative humidity percentage at a lower temperature. This also explains why windows are more often fogged up in the morning than in the evening.
What do you notice in practice?
- A higher reading on the hygrometer in the morning than before sleeping.
- Fogged-up windows or a clammy feeling on bedding when waking up.
- A slightly more stuffy feeling in the room upon waking.
What can you do about it?
A crack of ventilation, for example via a ventilation grille or a slightly opened window, already helps to limit the buildup of moisture during the night. Air out the bedroom well for a few minutes in the morning as soon as you wake up. If the bedroom remains structurally damp during the day, or if you notice fogged-up windows and a musty smell more often, the cause may be deeper, such as insufficient ventilation capacity for the number of occupants.
In that case, a dehumidifier can help keep moisture levels in check at night without having to leave the window wide open. Our advice is to run the Dynter AirPure DH251 on a quiet setting, so that the humidity does not rise more than desired during the night.
In short: increasing humidity at night is a normal result of breathing, less ventilation, and a lower temperature, but with the right measures, it does not have to lead to a damp or stuffy bedroom climate.