There are two humidity values: Relative Humidity (RH) and Absolute Humidity (AH).
The one you see everywhere on hygrometers or weather apps is relative humidity.

Relative humidity is the percentage of water vapor present in the air compared to the maximum amount the air can hold at a given temperature. For example, 50% relative humidity means the air is 50% saturated with water vapor. At 100%, the air is fully saturated and can’t hold any more moisture.

Absolute humidity, on the other hand, is the actual amount of water vapor present in a volume of air, expressed in grams per cubic meter (g/m³). It tells us how much water vapor is really in the air, regardless of the temperature.

For health and especially for keeping nasal mucosa moist it’s the absolute amount of water vapor that matters, not how saturated the air is. That’s why relative humidity is a poor indicator for those of us suffering from ENS. To know whether the air is humid enough for us, we need to convert relative humidity into absolute humidity.

Here is a graph showing absolute humidity values as a function of temperature for a given relative humidity.
To make things easier, I’ve created a Relative Humidity → Absolute Humidity converter.

Personally, I start to feel less discomfort and my nose feels less dry when the absolute humidity reaches around 12 g/m³ of water vapor, which corresponds to 70% RH at 20°C or 40% RH at 30°C. Of course, in my experience, the more water vapor there is in the air, the better I feel—perhaps up to a certain point.

So, only take into account the absolute humidity value to determine whether the air is humid enough for you or not.