What level of humidity is bad for health? A complete guide

September 22, 2025 •

4 min read

The U.S. Environmental Protection Agency (EPA) advises keeping indoor relative humidity below 60% to prevent mold growth. But what level of humidity is bad for health specifically, and how do both excessively high and low levels impact your well-being and home?

Quick Summary

Humidity outside the optimal 30-50% range poses significant health risks, fostering pathogen growth in moist conditions and irritating airways in dry air. Both extremes can heighten your susceptibility to illness, worsen allergies, and create discomfort.

Key Points

Ideal Range: The optimal indoor humidity for health and comfort is generally considered to be between 30% and 50%, but definitely below 60%.
High Humidity Risks: Humidity over 60% promotes the growth of mold, mildew, dust mites, bacteria, and viruses, which can trigger allergies and respiratory issues.
Low Humidity Risks: Dry air below 30% can irritate respiratory passages, dry out skin and eyes, and increase the spread of certain airborne viruses.
Allergy Impact: Both high and low humidity levels can exacerbate allergies, either by fostering allergens like mold and dust mites or by making allergens more easily airborne.
Solutions: Control high humidity with dehumidifiers or AC, and combat low humidity with humidifiers to keep your indoor air quality within a healthy range.

Understanding the Ideal Humidity Range

Most health experts and organizations like the EPA agree that the ideal indoor relative humidity (RH) is between 30% and 50%, or at least below 60%. When humidity falls outside this optimal range, it can trigger a cascade of negative effects on your health and home environment. Understanding these thresholds is the first step toward creating a healthier living space.

The dangers of high humidity (>60%)

When indoor humidity consistently rises above 60%, the environment becomes a fertile ground for biological pollutants that are harmful to your health. The effects can be both immediate and long-term.

Mold, mildew, and fungi

Perhaps the most well-known risk of high humidity is the proliferation of mold and mildew. These fungi thrive in damp conditions and can grow on various surfaces, including walls, ceilings, carpets, and upholstery. Inhaling or touching mold spores can trigger a range of health issues, especially for individuals with sensitivities.

Allergic reactions, such as sneezing, runny nose, and skin rashes
Asthma attacks, particularly in those with a pre-existing respiratory condition
Hypersensitivity pneumonitis, a serious lung inflammation in some cases

Dust mites

Dust mites are microscopic creatures that flourish in humid conditions. They feed on shed human skin cells and are a major cause of indoor allergies. Keeping humidity below 50% helps to inhibit their growth, reducing the concentration of these allergens in your home.

Increased transmission of viruses and bacteria

Research has shown that many viruses, including influenza, thrive in high-humidity environments. When the air is saturated with moisture, it can also lead to the proliferation of bacteria. This can increase the likelihood of respiratory infections.

Heat-related health issues

In hot weather, high humidity can prevent the body's natural cooling mechanism—sweating—from working efficiently. When sweat can't evaporate from the skin, you feel stickier and hotter, which can lead to heat exhaustion or even heatstroke in severe cases. Symptoms include fatigue, weakness, dizziness, and muscle cramps.

The dangers of low humidity (<30%)

While high humidity creates a breeding ground for pests and pathogens, air that is too dry also presents a different set of health challenges.

Respiratory tract irritation

Very dry air can irritate and dry out the mucous membranes in your nose and throat. This can make you more susceptible to colds, sinus infections, and the flu because your body's natural defenses are weakened. Symptoms often include a sore throat, dry cough, and nasal irritation.

Increased virus spread

Paradoxically, some viruses, including COVID-19, have been shown to remain viable and spread more effectively in low-humidity conditions. Dry air causes respiratory droplets to evaporate more quickly, leaving behind smaller, more concentrated particles that can travel farther and remain airborne longer.

Skin and eye discomfort

Dry air pulls moisture from your body, leading to dry, itchy, or chapped skin and lips. Contact lens wearers may experience increased eye irritation and dryness. In extreme cases, it can exacerbate conditions like eczema and psoriasis.

Exacerbated allergies

While dust mites thrive in high humidity, low humidity can worsen allergies by causing dust particles, pet dander, and pollen to become more easily airborne and suspended in the air. The dry environment also dries out and irritates nasal passages, making them more sensitive to allergens.

Comparison of high vs. low humidity health effects


Feature	High Humidity (>60%)	Low Humidity (<30%)
Primary Pathogens	Mold, mildew, fungi, bacteria	Airborne viruses
Physical Symptoms	Sticky skin, heat stress, fatigue	Dry skin, chapped lips, dry eyes
Respiratory Effects	Allergic reactions, asthma attacks	Irritated airways, dry cough, nosebleeds
Allergy Triggers	Dust mites, mold spores	Airborne dust, pollen, dander
Other Effects	Unpleasant odors, condensation	Static electricity, damage to wood furniture

How to manage indoor humidity levels

Controlling the humidity in your home is crucial for maintaining good health and protecting your property. Fortunately, a number of tools and strategies can help.

Managing high humidity

Use a dehumidifier: For consistently high humidity, a portable or whole-home dehumidifier can actively pull excess moisture from the air.
Ventilate properly: Use exhaust fans in kitchens and bathrooms to vent moist air outside. Also, ensure your home has proper ventilation to allow for a good exchange of air.
Run your air conditioner: Air conditioners are effective dehumidifiers because the cooling process removes moisture from the air as a byproduct.

Managing low humidity

Use a humidifier: A portable or whole-home humidifier can add essential moisture back into the air, especially during dry winter months.
Air-dry laundry indoors: The moisture evaporating from wet clothes can help raise the humidity level in a room.
Leave the bathroom door open: After a hot shower or bath, leaving the door open for a while can allow some of the moisture to distribute into the surrounding air.

Conclusion: Prioritizing a balanced indoor climate

Maintaining a balanced indoor humidity level is a simple yet effective way to protect your family's health and enhance your comfort. The question of what level of humidity is bad for health has a dual answer: both excessively high and low levels can create different but significant risks, from fostering mold growth to increasing viral transmission. By investing in a hygrometer to monitor your home's RH and using a dehumidifier or humidifier as needed, you can prevent these issues and ensure your living environment supports optimal health. It's a proactive step toward a healthier, more comfortable home. For more information on humidity's effect on allergies and asthma, the Asthma and Allergy Foundation of America is a great resource: Asthma and Allergy Foundation of America.

Frequently Asked Questions

When humidity is too high, your body's natural cooling process (sweating) is hindered, which can lead to heat stress, fatigue, and potential heat exhaustion. High moisture also encourages the growth of mold and dust mites, which can cause allergic reactions and asthma flare-ups.

Humidity levels consistently above 60% are considered unhealthy due to the promotion of mold, bacteria, and dust mites. Levels below 30% are also detrimental, as they can cause respiratory irritation and increase susceptibility to viral infections.

Yes, high humidity can make you sick, primarily indirectly. By creating a favorable environment for mold, mildew, bacteria, and dust mites, it can worsen allergies, trigger asthma attacks, and increase your risk of respiratory infections. It can also cause heat-related illnesses.

Signs of low humidity include dry, itchy skin; chapped lips; irritated sinuses and throat; static electricity; and an increased frequency of nosebleeds. Your furniture and floors might also show signs of drying, such as cracking wood.

Yes, poor humidity levels are directly linked to respiratory issues. High humidity can trigger mold allergies and asthma, while low humidity can dry out and irritate your respiratory tract, making you more vulnerable to infections.

Neither is better, as both high and low humidity levels are bad for health. The goal is to maintain a balanced, optimal humidity range of 30-50% to prevent the negative effects associated with each extreme.

The easiest way to check your home's humidity level is by purchasing an inexpensive device called a hygrometer. Many modern smart thermostats also have built-in hygrometers.