For vacation rental operators, one of the most challenging seasons of the year is the rainy season (tsuyu).

Running from June through July, this period brings high humidity and rising temperatures—the perfect combination for mold, unpleasant odors, and pest problems. Since vacation rentals often sit unattended for long stretches, insufficient preparation can lead to situations like “the whole room suddenly smells musty” or “a guest complains about a strange smell.”

The good news is that **just being a little more mindful during cleaning can significantly reduce the risks caused by humidity.** You don’t need special equipment or renovations—many effective measures cost nothing at all, or just a few hundred yen.

In this article, we’ll walk you through **”10 Rainy-Season Humidity Countermeasures”** that are genuinely useful in real-world vacation rental cleaning operations, covering both free and low-cost options. Every tip here is something cleaning staff and owners can put into practice right away, so be sure to read on.

1. Open the Windows and Ventilate Thoroughly (Free)

The most basic—and most effective—measure is ventilation. During the rainy season, the outside air is humid too, so you might think “there’s no point opening the windows.” But moving the air is far more effective against humidity than letting it sit still.

Immediately after checkout, a room tends to trap body heat, shower moisture, and cooking steam from the previous guest. During cleaning, always open all the windows for at least 5–10 minutes to fully exchange the air. The key is opening multiple windows or doors diagonally across the room to create a proper airflow.

2. Wipe Down Water Droplets in the Bathroom and Sink Area (Free)

The bathroom and sink area are the number-one source of mold growth. Pay special attention to tile grout, the area under shampoo bottles, and shelves where water tends to pool. Make it a standard rule to completely wipe away any water droplets during every cleaning session.

Wiping down walls and mirrors with a dry towel or squeegee **dramatically reduces the chance of mold caused by lingering moisture.** Simply running the exhaust fan isn’t enough—actually removing the moisture is what matters.

3. Prop Up Bedding to Let It Air Out and Release Trapped Moisture (Free)

Many vacation rentals only bother changing the sheets, but **the underside of mattresses and futons is where moisture tends to accumulate most.** Leave this unattended, and within a few months it can become a breeding ground for black mold.

During the rainy season, try propping futons against a wall to let air circulate during cleaning, or air them out in the sun when possible. Even if that’s difficult, simply opening a window for about an hour makes it much easier for internal moisture to escape.

4. Place Dehumidifying Packs in Closets and Storage Spaces (A Few Hundred Yen)

Dressers and closets tend to stay closed up, making them a hotspot for trapped humidity. If clothing picks up a musty smell, it directly affects guest satisfaction.

Place a store-bought dehumidifying pack (such as DryPet or silica-gel type) in each storage space. These can be found even at 100-yen shops, making them an extremely cost-effective solution. Check the contents every 2–3 months and replace any packs that have reached their moisture-absorption limit.

5. Use the Air Conditioner’s Dehumidify Mode (Electricity Cost Only)

On days when humidity spikes—even during vacant periods with no guests—running the air conditioner’s “dehumidify mode” (dry setting) for a few hours is a smart move. This is especially important for properties prone to musty odors or with poor natural ventilation, where managing indoor humidity is essential.

If possible, set a timer to run dehumidify mode for 2–3 hours after checkout or on heavy rain days. This can significantly cut down on that sticky, humid feeling and reduce mold risk indoors.

6. Regularly Clean the Rubber Seal Around the Refrigerator Door (Free)

A surprisingly overlooked spot is the rubber gasket around the refrigerator door. Condensation easily collects here, and because it’s a sealed, enclosed space, it becomes one of the prime zones for mold growth.

During cleaning, make it a habit to wipe down not just the inside of the fridge but also around the door with a cloth or alcohol wipe. The gasket area in particular tends to accumulate grime, so wiping it at least once a week is ideal.

7. Use a Circulator or Fan to Keep Air Moving (Approx. ¥2,000–5,000)

If your budget allows for an appliance purchase, setting up a small circulator or an oscillating fan can be a highly effective humidity countermeasure. Even blowing air through an empty room can dramatically change the odds of mold developing.

It’s especially worth setting up a system to regularly circulate air into closets or bedrooms with few windows, where air tends to stagnate. Using it alongside the air conditioner boosts the dehumidifying effect even further.

8. Regularly Clean Exhaust Fan and Bathroom Dryer Filters (Free)

Even if you think you’re ventilating properly, a clogged filter on an exhaust fan or bathroom dryer means the air isn’t actually moving much at all. This leaves you “thinking” you’ve ventilated when in reality you haven’t—which ultimately leads to mold and odor problems.

Every 2–3 months, remove the filters from the bathroom dryer and range hood and rinse them with water. This only takes about 10–15 minutes but makes a huge difference in air circulation.

9. Choose Charcoal-Based Deodorizers Over Air Fresheners for Odor Control Plus Moisture Absorption (From ¥300)

Many vacation rentals use air fresheners, but masking humidity-related odors with fragrance isn’t the answer—actually absorbing the odor is what matters. We recommend deodorizers that combine odor absorption and moisture control, made with activated carbon or bamboo charcoal.

Placing one in the bathroom, entryway shoe cabinet, closet, and under the bed will absorb both odors and moisture. These are consumable items, but since they only need replacing every 1–2 months, the cost-effectiveness is quite good.

10. Create a Checklist and Share It With Cleaning Staff (Free)

Humidity control can’t rely on “whoever notices, handles it.” It’s essential to create a checklist so every staff member follows the same standard.

For example, try creating a printed sheet with checkboxes covering items such as “wipe bathroom walls with a squeegee,” “prop up futons to air them out,” and “check the condition of dehumidifying packs”—then have staff record their completion after each cleaning session.

These small habits—whether they’re actually done or not—make a huge difference in how a room holds up during the rainy season.

Conclusion

Left unchecked, rainy-season humidity can lead to mold, unpleasant odors, and a serious drop in guest ratings. But by simply adjusting your mindset during everyday cleaning, you can keep these risks firmly under control. The 10 humidity countermeasures introduced here range from completely free habits to small investments of a few hundred to a few thousand yen—offering a variety of practical approaches.

• Free techniques like window ventilation, wiping away water droplets, and airing out bedding
• Affordable, easy-to-adopt items like dehumidifying packs, fans, and deodorizers
• Structural improvements like filter cleaning routines and checklist systems

Combining these measures makes it possible to maintain a clean, comfortable guest experience even during the rainy season. To avoid reviews mentioning “musty smell” or “felt damp and uncomfortable,” start today with whatever you can put into practice right now.

Let Stay Buddy Handle Your Rainy-Season Vacation Rental Operations

“I’m worried about odors during the rainy season,” “Guests keep complaining about humidity,” “I’m not sure if our dehumidification and mold prevention measures are really up to par”—if you’re a vacation rental owner facing concerns like these, please reach out to Stay Buddy Co., Ltd. for a consultation. From practical, on-the-ground humidity control advice to staff training, checklist development, and product selection, we offer comprehensive support from a professional perspective. Waiting until mold or odors appear is already too late—let’s start preparing thoroughly together, starting now.