For owners and property managers, “tsuyu” (Japan’s rainy season) is one of the trickiest times of year. During this extended period of rain and high humidity, vacation rental management and guest experience face a range of challenges. The most common issues include musty, damp rooms, mold growth, and condensation damage.

For guests, nothing ruins a trip faster than a moldy-smelling room or laundry that won’t dry due to humidity—it’s pure stress on an otherwise enjoyable stay. For owners, mold damage and unpleasant odors can drag down review scores, directly impacting long-term revenue. In this article, we’ll walk through three essential humidity control strategies every rainy-season vacation rental operator should know.

Over years of managing vacation rentals, we’ve seen no shortage of cases where poor rainy-season preparation led to mold outbreaks requiring wallpaper and furniture repairs, or resulted in negative guest reviews. Since the rainy season comes around every year without fail, putting consistent countermeasures in place is the key to maintaining guest satisfaction and preserving your property’s value over the long term.

1. Why Rainy-Season Humidity Control Matters

During Japan’s rainy season (roughly June through July), rain persists across the country and humidity climbs to very high levels. For vacation rental operators, the negative effects of this high humidity are far from trivial.

• Mold growth
  Poorly ventilated spots—behind wallpaper, on ceilings, behind furniture—become prime breeding grounds for mold. When mold spreads to futons and curtains, it creates both health risks and serious discomfort for guests.
• Furniture and appliance deterioration
  High humidity can warp wooden furniture and cause internal moisture damage to appliances. If frequently-used equipment like air conditioners or air purifiers breaks down, that leads straight to guest complaints.
• Unpleasant odors and stuffy air
  Rooms saturated with humidity tend to feel heavy and carry that distinctive “musty” smell. If a guest is hit with an unpleasant odor the moment they walk in, it colors their entire impression of the stay.
• Lower guest satisfaction
  Whether guests can stay comfortable during the rainy season has a major effect on your reviews. Leaving humidity and mold issues unaddressed invites poor ratings, which in turn hurts your occupancy rate.

Minimizing these risks requires operators to get ahead of the problem with proactive humidity control. In the next section, we’ll introduce three concrete strategies, along with key considerations and implementation tips for each.

2. Strategy 1: Thorough Ventilation and Dehumidification

2-1. Ventilation Basics: Natural vs. Mechanical Ventilation

The most fundamental humidity countermeasure is regular ventilation. If you keep the property sealed up just because it’s raining throughout the season, indoor moisture will build up and create ideal conditions for mold and dust mites. Whenever there’s a break in the rain—sunny or even just overcast skies—make it a habit to open the windows and let air circulate.

Some properties don’t have enough windows for adequate natural ventilation, so it’s worth running the bathroom or toilet exhaust fan around the clock, or installing a circulator fan or ventilator in the living room to force air movement. It’s also considerate to include a note for guests, such as “please turn off the air conditioner while windows are open,” to help avoid wasted energy.

2-2. Dehumidifiers and Air Conditioner Dry Mode

Installing a dehumidifier is one of the most effective rainy-season measures available. Use a powerful unit for larger spaces like the living room or bedroom, and place compact dehumidifiers or moisture-absorbing packs in tighter spots like closets or shoe cabinets.

Most air conditioners also come with a dehumidify (dry) mode, so it’s worth recommending that guests keep a consistent level of dehumidification running—whether they’re out for the day or staying in. That said, since this can increase electricity costs, it’s a good idea to provide clear guidelines guests can understand, such as “use as needed” or “avoid running for extended periods.”

2-3. Preventing Condensation Around Windows and Doors

This applies to winter as much as the rainy season, but condensation creates a breeding ground for mold.

Physical solutions—like installing double-pane windows or applying insulating film—help reduce the temperature difference with the outside air. It’s also effective to regularly wipe down window sashes and treat them with rubbing alcohol or anti-mold spray. During a guest’s stay, it also helps to include a note like “please wipe away any condensation that forms.”

3. Strategy 2: Using Anti-Mold and Deodorizing Products

3-1. Mold Removers and Anti-Mold Sprays

When humidity is high, mold can spread astonishingly fast. Pay special attention to bathrooms, sinks, kitchens, and the inside of air conditioners—anywhere with water exposure or temperature fluctuations. Beyond using a mold remover during regular cleaning, applying anti-mold spray in trouble spots can help suppress growth before it starts.

It’s reassuring to give your cleaning staff a clear checklist—for instance, “prioritize checking for mold during the rainy season” or “carefully inspect for any black or pink discoloration”—along with a system for reporting issues.

3-2. Placing Dehumidifying Agents and Charcoal

Poorly ventilated spaces like closets, shoe cabinets, and storage areas benefit from commercial dehumidifying agents (pot-type or sheet-type products).

Placing charcoal (such as binchotan or bamboo charcoal), known for its moisture-regulating properties, is another great option—it naturally absorbs both humidity and odors. Keeping up with these measures helps reduce complaints like “the closet feels damp and unusable.”

3-3. Using Deodorizers and Air Fresheners

High humidity can trap odors in a room, and it’s particularly common for carpets and fabric sofas to develop unpleasant smells.

Regular odor maintenance with deodorizing sprays, charcoal-infused deodorizers, or air fresheners is important—but overusing strongly scented air fresheners can actually bother some guests. It’s best to strike a balance by choosing unscented deodorizers or subtle, natural aroma options.

4. Strategy 3: Rethinking Linen and Towel Management

4-1. Thorough Washing and Drying

During the rainy season, linens and towels dry more slowly, increasing the risk of bacteria and mold growth. Storing items that are only partially dry after washing produces a distinctly unpleasant smell that often leads to guest complaints.

Make sure to dry items completely using a dryer or a dehumidifier designed for indoor drying. This matters especially for sheets and pillowcases, which absorb body oils and sweat—if they’re not thoroughly dried, mold and dust mites can multiply quickly.

4-2. Managing Linen Stock by Room

It’s reassuring to build a habit of inspecting guest towels and bedding regularly during the rainy season, checking specifically for mold odors or discoloration caused by moisture. If you manage multiple properties, allocating and tracking inventory by room—so clean linens can always be restocked when needed—will pay off in better reviews.

4-3. Sharing Backup Solutions with Guests

For long-term guests, or in case sudden rain prevents laundry from drying, guests will appreciate clear guidance on things like indoor drying racks, dehumidifiers, or how to use a washing machine’s dryer function. Providing an English-language manual or a photo-based step guide in the room makes things easier for international guests too, reducing troubles and questions—and easing the burden on you as the owner.

5. Providing Guest Information and Setting House Rules

5-1. Sharing Rainy-Season Tips in Pre-Arrival Messages

It’s a good idea to include rainy-season precautions in your welcome message or house guide sent after booking confirmation. Even brief notes—like encouraging guests to crack open a window for ventilation, or explaining how to wash and dry laundry during a longer stay—help guests understand what to expect and cut down on unnecessary questions.

Another good approach is adding rainy-season-specific advice to your house rules—things like “please wipe away any condensation that forms,” “using the air conditioner’s dehumidify function will keep the room comfortable,” or “turn on the dehumidifier when drying laundry indoors.” Many guests are experiencing Japan’s rainy season for the first time, so they may be unfamiliar with how to operate the air conditioning or handle laundry.

5-3. Prioritizing Communication

Sensitivity to humidity-related discomfort varies from person to person. If a guest notices something like a musty smell or finds the room too damp to sleep comfortably, offering an easy way to reach out can prevent small issues from escalating. Let guests know they can contact you via message or phone, and even if round-the-clock availability isn’t realistic, showing a commitment to responding promptly goes a long way toward building trust.

6. Long-Term Rainy-Season Solutions and Renovation

6-1. Insulation and Waterproofing Renovations

Some properties may need more fundamental insulation or waterproofing renovations. If water leaking through exterior walls or seeping in from a balcony is causing mold or wood rot, quick fixes alone are unlikely to solve the problem for good. Large-scale renovations come with a cost, but from a long-term perspective, they represent an important investment in preserving property value and boosting guest satisfaction.

6-2. Choosing the Right Flooring and Wallpaper

Selecting moisture-resistant flooring (such as high water-resistance flooring options) or wallpaper with anti-mold and moisture-control properties can significantly reduce mold and damage during the rainy season. It’s worth considering these materials whenever you’re planning an interior renovation. This is especially important around water-use areas and entryways, where wet shoes and umbrellas often bring moisture indoors—waterproof materials are a smart choice there.

6-3. Considering the Exterior and Surrounding Environment

For standalone houses or cottage-style rentals, it’s important to factor in rainwater drainage around the garden and exterior grounds. Poor drainage raises humidity levels around the building, creating a risk of mold or termite infestation from the foundation up. Be sure not to overlook exterior maintenance—inspecting drainage channels, improving soil conditions, and regularly maintaining the roof and gutters.

Leave Your Rainy-Season Vacation Rental Prep to Stay Buddy Inc.!

The rainy season is a distinctly Japanese climate phenomenon, and how well you navigate this humid stretch directly affects both guest satisfaction and revenue stability. Mold and odor problems can quickly frustrate guests and lead to negative reviews, which is why early, proactive measures and ongoing maintenance are absolutely essential.

If you’re thinking “I want to tackle humidity control properly but don’t know where to start,” or “I’d like to leave day-to-day cleaning and facility management to the professionals,” we’d love for you to reach out to Stay Buddy Inc. Drawing on years of hands-on vacation rental management experience, we provide comprehensive support—from rainy-season mold prevention to everyday guest communication. Let’s work together to create a comfortable environment your guests will love.