Yes, 87% humidity is very high, whether you’re talking about the air outside or inside your home. The EPA recommends keeping indoor relative humidity between 30% and 50%, and no higher than 60%. At 87%, you’re well past the threshold where moisture starts causing problems for your health, your home, and your comfort.
What 87% Humidity Actually Means
Relative humidity measures how much water vapor the air is holding compared to the maximum it could hold at that temperature. At 87%, the air is nearly saturated. It can barely absorb any more moisture, which is why sweat doesn’t evaporate well off your skin and everything feels damp and sticky.
The National Weather Service uses dew point rather than relative humidity to gauge comfort because it’s more consistent throughout the day. But as a rule of thumb, when relative humidity stays above 80% for extended periods, conditions feel oppressive. Dew points above 65°F are considered uncomfortably muggy, and 87% humidity at warm temperatures almost always corresponds to dew points in that range or higher.
How It Affects How Hot You Feel
High humidity makes warm air feel dramatically hotter. Your body cools itself by evaporating sweat, and when the air is already holding that much moisture, evaporation slows to a crawl. The result is a “heat index,” or feels-like temperature, that can be far above the actual air temperature.
At 80°F with 80% humidity, the heat index jumps to 86°F. At 90°F, it shoots up to 113°F. Since 87% humidity is even higher than those chart values, the perceived temperature would be more extreme still. That puts you squarely in the danger zone for heat exhaustion and heat stroke during physical activity, especially if you’re outdoors for extended periods.
Health Risks at This Humidity Level
Prolonged exposure to very high humidity creates several overlapping health problems. The most immediate is heat stress: your body can’t cool itself efficiently, so your core temperature rises. This leads to fatigue, headaches, dizziness, and in serious cases, heat-related illness.
The longer-term concern is respiratory health. Indoor environments at 87% humidity are ideal breeding grounds for mold, dust mites, and bacteria. Research published in Environmental Health Perspectives found that dampness and mold in buildings are linked to 30 to 50% increases in respiratory and asthma-related health outcomes. Residential dampness is also associated with 8 to 20% of respiratory infections in the U.S. The health effects go beyond people with allergies. Mold and microbial growth trigger inflammatory responses even in people who aren’t allergic, causing cough, wheezing, nasal congestion, and throat irritation through non-allergic pathways.
When multiple types of mold and bacteria grow together in damp conditions, their effects can be worse than any single species alone. Studies have shown that these organisms interact synergistically, meaning their combined immune-suppressing and inflammatory effects are amplified.
Sleep Gets Worse
If your bedroom sits at 87% humidity, expect poor sleep. Research on humid heat exposure during sleep found that high humidity combined with warm temperatures suppresses both deep sleep and REM sleep, the two stages your body needs most for physical recovery and memory processing. Core body temperature stays elevated instead of dropping the way it normally does at night, and you wake up more frequently. The result is less restorative sleep even if you spend the same number of hours in bed.
Your Home Takes Damage Too
Mold begins growing on building materials when relative humidity stays above 70 to 80%. At 87%, you’re giving mold nearly ideal conditions. It can colonize drywall, wood, carpet, ceiling tiles, and fabric within days if the humidity persists. Beyond visible mold, sustained high moisture causes paint to peel, wood to warp, metal to corrode, and musty odors to permeate soft furnishings. Electronics are also vulnerable, as condensation on circuit boards can cause short circuits and corrosion over time.
How to Bring It Down Indoors
If your indoor humidity is reading 87%, a dehumidifier is the most direct solution. For rooms up to about 500 square feet at that humidity level, a 30-pint-per-day unit is typically sufficient. For spaces around 1,000 square feet, you’ll want a 40 to 50-pint model. Larger areas or whole basements in consistently damp climates may need a 60-pint large-capacity dehumidifier.
A few other steps help bring humidity down and keep it there:
- Ventilation: Run exhaust fans in bathrooms and kitchens during and after showers or cooking. These are the biggest indoor moisture sources.
- Air conditioning: AC units naturally dehumidify as they cool. Running your system consistently is often enough to keep humidity below 60% in moderate climates.
- Air sealing: In humid climates, outdoor moisture seeps in through gaps around windows, doors, and foundations. Sealing these reduces the moisture load your dehumidifier or AC has to handle.
- Drainage: Make sure gutters direct water away from your foundation and that crawl spaces have vapor barriers. Ground moisture migrating into your home is a common cause of persistently high indoor humidity.
Your target is 30 to 50% relative humidity indoors. A basic hygrometer (available for under $15) lets you monitor levels in different rooms. Basements and bathrooms tend to run highest, so check those first. Getting from 87% down to a healthy range may take a combination of approaches, but the improvement in comfort, air quality, and sleep is significant once you get there.