The Key to Preventing Mildew in the Summer, According to Cleaning Pros

Warm weather may mean more time outdoors, but it can also create the perfect conditions for mildew indoors. Bathrooms, basements, laundry rooms, and other damp areas often become breeding grounds for the pesky problem during the summer months, especially when humidity levels rise.

Mildew is a type of fungus that typically appears as white or gray powdery spots on surfaces like shower walls, windowsills, and grout. While it’s often grouped together with mold, mildew tends to remain on the surface, whereas mold can penetrate deeper into materials and become more difficult to remove, says Dan DiClerico, director of the Good Housekeeping Institute Home Improvement & Outdoor Lab.

If it seems like mildew appears out of nowhere once the weather heats up, you’re not imagining it. Warm temperatures and excess moisture create the ideal environment for growth. “Mildew thrives in warm, damp conditions, which are more common in the summer months,” says DiClerico.

High humidity, steamy showers, wet towels, damp swimsuits, and poor airflow can all contribute to excess moisture indoors. The biggest mistake you can make? Letting moisture linger. When that moisture stays on surfaces, mildew can begin to grow quickly—especially in bathrooms, basements, laundry rooms, and other areas that don’t dry out easily.

“Proper ventilation is key to preventing mildew,” says DiClerico.

These expert-backed habits can help keep mildew from taking hold, even during the most humid months of the year.

• Improve ventilation: Bathrooms are one of the most common places for mildew to develop, because moisture tends to hang around long after a shower ends. If your bathroom has an exhaust fan, DiClerico recommends running it for at least 20 minutes after showering, especially on muggy days. And if you don’t have a fan? Open a window for an hour or so to help humid air escape, he says. The same applies to other moisture-prone areas, including laundry rooms and basements. The more airflow you create, the harder it is for mildew to thrive.
• Keep humidity levels in check. Humidity is one of the biggest drivers of mildew growth, so running a dehumidifier in damp spaces, particularly basements, can help keep moisture levels under control. Aim to keep indoor humidity below 50%, says DiClerico. Once humidity rises above that threshold, mildew, mold, and other microorganisms have a much easier time multiplying.
• Dry damp surfaces and fabrics promptly. Mildew thrives when moisture sits on surfaces for extended periods. After showering, consider squeegeeing shower walls, doors, and tubs to help them dry faster. It’s also important to avoid leaving wet towels, swimsuits, workout clothes, or cleaning rags piled up in hampers, gym bags, or closets. The sooner damp fabrics air out or make it into the wash, the better.

• Stay ahead of leaks. Even a small leak can create the damp conditions mildew needs to grow. Regularly check under sinks, around toilets, near washing machines, and around windows for signs of moisture or water damage to help prevent mildew from becoming a recurring problem.
• Clean mildew-prone areas more frequently. During particularly humid stretches in the summer, mildew can grow faster than usual. To stay ahead of it, clean moisture-prone areas like showers, tubs, grout lines, and windowsills regularly using a mold and mildew remover in areas where moisture tends to accumulate.
• Be mindful of what you store in damp spaces. Basements and attics can become even more humid during the summer, making them less-than-ideal storage spaces for items sensitive to moisture. Whenever possible, avoid storing linens, books, cardboard boxes, or upholstered furniture in areas that tend to feel damp. If you do need to use these spaces for storage, a dehumidifier can help reduce excess moisture and lower the risk of mildew growth.

Despite your best efforts, mildew may still pop up, particularly during the more humid summer months. The key is to address it before it spreads.

Small, surface-level mildew (generally under about 10 square feet, says DiClerico) can usually be handled at home with a cleaner specifically formulated for mold and mildew, like top-tested CLR Mold & Mildew Stain Clear Stain Remover.

If it keeps coming back, covers a larger area, or comes with a persistent musty smell, it may signal a deeper moisture problem that needs professional attention.