A humidity level of 63% is considered high for indoor environments. The EPA recommends keeping indoor relative humidity between 30% and 50%, with an absolute ceiling of 60%. At 63%, you’ve crossed that threshold, and the excess moisture can affect your comfort, your health, and your home. Outdoors, 63% may or may not feel uncomfortable depending on the temperature.
Why 63% Is Too High Indoors
The EPA’s guidance is clear: indoor relative humidity should stay below 60%, ideally in the 30% to 50% range. At 63%, you’re in territory where moisture-related problems start compounding. Mold spores germinate more readily, building materials absorb moisture, and the air itself starts to feel heavy and stale.
Dust mites are one of the first problems to escalate. These microscopic creatures need humidity above the 40% to 50% range to survive, and their populations increase substantially as humidity climbs beyond that point. At 63%, you’re providing ideal breeding conditions. For anyone with allergies or asthma, this is a meaningful difference, not just a number on a hygrometer.
How It Affects Your Body
High humidity doesn’t just make a room feel stuffy. Research published in Respiratory Research found that higher relative humidity is negatively associated with lung function and increases the risk of obstructive lung disease. It can also trigger bronchospasm by amplifying allergen exposure, worsening symptoms for people with asthma or COPD. Even short-term exposure to elevated humidity has been linked to restrictive breathing patterns.
Sleep takes a hit too. A study examining humid heat exposure during nighttime sleep found that when humidity reached 75% at warm temperatures, deep sleep (stage 3) and REM sleep both decreased significantly compared to drier conditions. The body struggles to cool itself through sweat evaporation when the surrounding air is already saturated with moisture. At 63%, you’re not at the extreme tested in that study, but you’re trending in the wrong direction, especially during summer months when bedroom temperatures are already elevated.
Outdoors, 63% Tells You Less Than You Think
Relative humidity is, as the name suggests, relative. It describes how much moisture the air holds compared to its maximum capacity at a given temperature. The same 63% reading feels completely different at 65°F than it does at 90°F, because warmer air holds far more total moisture. This is why the National Weather Service recommends looking at dew point rather than relative humidity to judge outdoor comfort.
The dew point comfort scale works like this:
- 55°F or below: dry and comfortable
- 55°F to 65°F: becoming sticky, with muggy evenings
- 65°F and above: oppressive, with lots of moisture in the air
So if it’s 85°F outside with 63% relative humidity, the dew point is around 70°F, which falls into the oppressive category. But if it’s 70°F with 63% humidity, the dew point sits near 56°F, barely into the “sticky” range. The percentage alone doesn’t capture how the air actually feels on your skin.
Getting Humidity Below 60%
If your indoor reading consistently sits at 63% or above, a dehumidifier is the most direct fix. Set it to maintain humidity between 30% and 50%. The key is matching the unit’s capacity to your space. A small portable unit won’t make a dent in a large basement, so check the square footage rating before buying. Compressor dehumidifiers work best in warm climates, while desiccant models perform better in cooler temperatures.
Beyond dehumidifiers, a few habits make a real difference. Run exhaust fans while cooking and showering. Make sure your dryer vents to the outside, not into a garage or crawl space. Check that your air conditioning system is draining properly, since a functioning AC unit pulls moisture from the air as a byproduct of cooling. If you notice condensation forming on windows, that’s a visual confirmation that indoor humidity is too high and moisture is actively looking for surfaces to settle on.
In homes without air conditioning, airflow matters. Opening windows on opposite sides of the house creates cross-ventilation that helps carry moisture out, though this only works when outdoor humidity is lower than indoor levels. On muggy days, keeping windows closed and running a dehumidifier is the better strategy.
The Risks of Staying at 63%
A single afternoon at 63% humidity won’t cause mold to bloom across your walls. The concern is sustained exposure. Mold colonies need consistent moisture over days or weeks to establish themselves, and they tend to start in hidden spots: behind drywall, under carpet padding, inside HVAC ducts. By the time you see visible mold, the colony has often been growing for a while.
Wood furniture, musical instruments, books, and electronics are all sensitive to prolonged humidity above 60%. Wood swells and warps. Paper products develop a musty smell. Electronics can experience corrosion on internal components. If you store anything valuable in a basement or attic, monitoring humidity in those spaces is especially important, since they tend to run higher than the rest of the house.
For most people, bringing indoor humidity down from 63% to the 45% to 50% range produces a noticeable improvement in comfort within hours. The air feels lighter, fabrics feel drier, and sleeping becomes easier. It’s a relatively small adjustment on paper, but the difference in how a room feels is surprisingly large.