Three weeks after the water left, her son started wheezing at night

A typical scenario based on situations we commonly see. Names and details are illustrative.

Nid lives in a two-storey house in Khlong Toei, Hat Yai district, Songkhla, with her husband, her six-year-old son Phum and her 72-year-old mother. Phum has had asthma since he was three, and his grandmother has long-standing allergic rhinitis. At the end of the year, after days of heavy rain, the ground floor flooded to about forearm depth for four days. The family moved upstairs. Phum's mattress, pillows and soft toys were all on the upper floor and stayed dry, and Nid felt lucky the damage was limited.

Once the water drained, everyone pitched in: washing the ground floor, scrubbing, wiping cabinets and drying out wet belongings. Within a week the house looked fine. But in the third week, strange things started. Phum coughed at night several nights in a row, and one night needed his reliever inhaler at 2 a.m. Grandma sneezed every morning with a nose that would not stop running. Nid herself developed an itchy rash on her arms. And late one night, switching on the kitchen light, she saw cockroaches scatter from under the sink and behind the fridge, something she had never seen in this house before.

"The water never reached the bedrooms," she said. "Why is his asthma worse?" At the hospital, the doctor explained that after a flood, indoor humidity stays high for weeks. That lets dust mites in bedding and mould in the house multiply, while cockroaches escaping flooded drains move indoors. All of these are allergens that can trigger asthma. The doctor adjusted Phum's medication and told Nid to deal seriously with the home environment.

Nid's story points to a problem many families miss. We tend to think flood danger ends when the water drains and the house dries. In reality, the weeks after the flood are when indoor allergens quietly build up, hitting children, older people and anyone with allergies or asthma hardest. This article explains how dust mites and cockroaches are linked to flooding, why insecticide sprays and sweeping are not enough, and how WHD's residential ozone disinfection service fits into a recovery plan, including an honest account of what ozone does and what needs other methods.

The allergens that multiply after the water drops

Dust mites: tiny creatures that love humidity

Dust mites are microscopic relatives of spiders, invisible to the naked eye. They live in mattresses, pillows, blankets, fabric sofas, carpets, curtains and soft toys, feeding on skin flakes shed by people and pets. Mites do not drink; they absorb moisture from the air. So they multiply quickly in humid homes and decline when the air is dry. A house after a flood, with walls, floors and furniture slowly releasing moisture for weeks, is mite paradise, even if the bedroom itself never got wet.

It is not the mite itself that causes allergy but proteins in its droppings and body fragments. These particles are small and light, puffing into the air when we turn over in bed, plump a pillow or sweep, and landing in our noses and airways. Crucially, the allergen remains even after the mites die, so control means both reducing the mites and removing what they leave behind.

Cockroaches: refugees from the drains

Many cockroaches live in drains, manholes and damp underground spaces. When floodwater fills the drains, they flee upward and into homes through floor drains, gaps under doors and cracks in walls. After the water drops, a damp house with food scraps and dark hiding places under the sink, behind the fridge or inside swollen kitchen cabinets becomes their ideal new home.

Cockroaches cause trouble in two ways. First, as allergens: proteins in their saliva, droppings and shed skins are important triggers for asthma and allergy, especially in children living in cities. These accumulate in dust on kitchen floors, under furniture and inside cupboards. Second, as carriers: they walk through sewage and waste, then across counters, dishes and food, potentially spreading diarrhoea-causing bacteria such as Salmonella and E. coli.

Mould: the accelerant working alongside them

The same humidity that feeds mites feeds mould. Mould can begin growing within 24 to 48 hours of materials getting wet, as the WHO and US CDC warn. Mould spores are another allergen group, and some moulds are even food for dust mites. A house with humidity, mould, mites and cockroaches at the same time exposes the family to several allergens at once.

Symptoms to watch for

• Repeated morning sneezing, runny or blocked nose, itchy nose and eyes, red eyes
• A persistent cough, especially at night or early morning
• Wheezing, chest tightness or breathlessness in people with asthma
• Eczema flares, itching in skin folds, arms and legs
• Poor sleep and night waking, leaving children drowsy and unfocused by day
• Diarrhoea or stomach pain if food or dishes were contaminated by cockroaches

Severe breathlessness, blue lips or an attack that does not respond to the inhaler means going to hospital immediately. Anyone with high fever or calf pain after wading through floodwater should also consider leptospirosis and see a doctor quickly. Managing the home reduces triggers; it does not treat disease.

Who is most at risk

• Children with asthma or allergies, whose airways are sensitive and who spend a lot of time on floors and beds.
• Babies, who lie on mattresses, cushions and blankets most of the day.
• Older adults with chronic rhinitis, COPD or heart disease.
• Pregnant women, whose allergies may flare while some medicines must be used with care.
• People with eczema, for whom dust mites are a major trigger.

The impact goes well beyond sneezing

Health: old conditions flare, new ones begin

For people who already have asthma or allergies, the post-flood period is often the worst time of year: more frequent inhaler use, sometimes emergency visits in the middle of the night. For people who never had symptoms, weeks of heavy exposure can bring on chronic sneezing and congestion for the first time.

Money: medicines, doctor visits and replacements

Inhalers, antihistamines, clinic visits and emergency room bills add up, before counting insecticide bought every week and new mattresses and pillows bought without fixing bedroom humidity, which soon fill with mites again.

Time and sleep

A child coughing all night means parents awake all night too. Adults go to work exhausted, children go to school drowsy, and some parents take repeated days off for doctor visits in a single month. Quality of life drops for the whole family, often without anyone linking it to the flood.

How you feel about your home

Seeing cockroaches in the kitchen at night makes many people feel their home is dirty. They avoid cooking, won't leave food out and feel embarrassed when guests visit. Feeling unsafe in your own home is a stress that piles on top of the flood itself.

Why familiar methods do not stop the allergies

Spraying insecticide into every corner. Sprays may kill the cockroaches they hit, but the chemical mist is another airway irritant for an asthmatic child. And dead cockroaches, droppings and shed skins remain allergenic unless they are properly cleaned away.

Sweeping with a broom and dusting with a dry cloth. This launches allergen-laden dust into the air, where it settles again on beds and furniture. Sensitive people often feel worse during or after cleaning.

Vacuums without fine filtration. Some vacuums suck dust in and blow the smallest particles straight back out of the exhaust.

A quick session in the sun for the mattress. Sun dries the surface, but if exposure is short or the mattress goes back into a damp room, mites deep inside survive and the accumulated allergen is never washed out.

Relying only on an air purifier. Purifiers trap particles floating in the air, but most mite and cockroach allergen is heavy and settles fast into beds, carpets and corners the purifier cannot reach, and humidity stays just as high.

Incense or air freshener to cover mustiness. Smoke and fragrance add more airway irritants while the cause of the smell remains.

Painting over mouldy or damp walls. Mould keeps growing under the paint, and trapped moisture keeps feeding mites.

Post-flood allergen control has to work on several fronts at once: lowering humidity, removing cockroach food and hiding places, removing accumulated allergen, and killing mould and bacteria in the air and corners. No single method covers all of that.

Where WHD ozone disinfection fits for allergy-prone households

Ozone (O₃) is a strongly oxidising gas. Released into a sealed room, it spreads everywhere, including under beds, behind cabinets, inside storage spaces and corners that cloths and vacuums cannot reach. It breaks down the cell structures of viruses, bacteria and mould, and breaks apart odour molecules such as damp mustiness and the stale smell cockroaches leave behind. It then reverts to oxygen (O₂) with no chemical residue, a real advantage in homes where people react to chemicals and fragrances.

According to the test results the company has had certified by Thailand's Department of Medical Sciences and Intertek (UK), WHD's ozone treatment eliminates viruses, bacteria and mould by 99.99%. See our certification page.

Ozone does not replace washing, drying, laundering bedding or medical care. People with allergies or asthma should keep taking medication as prescribed alongside improving the home.

Our process

1. Learning about the home and the family. Floor area, rooms, flood level, where cockroaches appear, and whether anyone has asthma or allergies, so we can plan room order and ventilation time carefully.
2. Readiness check. The house has been washed and is reasonably dry, bedding has been laundered, and cockroach control or crack sealing is done or clearly planned.
3. Preparing the space. Everyone, pets and plants leave; opened food goes into sealed containers; cupboards, drawers and wardrobes are opened; doors and windows closed.
4. Filling rooms with ozone, covering bedrooms, living areas and the kitchen where cockroaches hide.
5. Contact time. A typical cycle is about 30 minutes per zone.
6. Rest and ventilation. Ozone reverts to oxygen, windows open, and the team confirms when it is safe to go back in.
7. Ongoing care advice. Humidity control, dust-free cleaning methods and keeping cockroaches out.

For extra surface disinfection in the kitchen and dining area, combine with WHD's disinfection spraying service. Ozone jobs from 15,000 baht also receive a free medical-grade disinfectant spray for counters and high-touch surfaces.

10 reasons to include ozone in your post-flood allergen plan

1. Fewer airborne mould spores, an allergen that arrives with post-flood humidity and works alongside dust mites.
2. No chemical residue, ideal for homes with asthmatic children and people sensitive to cleaning products.
3. It reaches under beds, behind cupboards and into kitchen gaps where dust and cockroach residue collect.
4. It clears stale cockroach and musty odours by breaking down odour molecules, with no incense or perfume to irritate noses.
5. It kills bacteria cockroaches bring in around kitchen corners and food preparation areas, as a step after wiping surfaces.
6. Certified test results. According to the company's certified results from the Department of Medical Sciences and Intertek, it eliminates viruses, bacteria and mould by 99.99%. See the ozone disinfection service.
7. Quick. About 30 minutes per zone plus rest and ventilation; the family can plan just half a day out.
8. It protects your investment in new bedding, so mite-proof covers and new pillows are not reclaimed by mould and old smells.
9. A structured fresh start, with the team helping you sequence the steps instead of trial and error with a dozen products.
10. A team that understands households with respiratory conditions, planning rest and ventilation time with care. Talk to us via the residential ozone page.

Before and after: a home with fewer allergy triggers

Note: individual symptoms depend on many factors; keep following your doctor's treatment. Environmental results depend on humidity control and consistent care after treatment.

Example case: Nid's home in Hat Yai

An illustrative example to explain the process, not a review from an identified customer.

Back from the hospital, Nid contacted WHD on LINE and explained that the household included an asthmatic child and an older adult with allergies. The team suggested a three-phase plan. Phase one tackled the sources: hot-wash sheets, pillowcases and blankets; switch Phum's mattress and pillow to mite-proof covers; box up most of the soft toys; run a dehumidifier in the bedroom. Phase two dealt with cockroaches: her husband removed the swollen under-sink cabinet, sealed the crack beside the waste pipe, fitted floor-drain covers, moved food into airtight containers and hired a pest control company to place bait where roaches were seen. Droppings and residue were wiped up with damp cloths instead of swept.

Phase three was ozone day. Nid took the whole family to a nearby mall in the morning. The team divided the house into four zones: Phum and Grandma's bedroom, the main bedroom, the living room, and the kitchen with the storeroom. Each zone ran about 30 minutes, followed by rest and ventilation. Because of Phum's asthma, the team advised leaving the bedroom windows open for a good while longer before bedtime.

When they returned in the afternoon, Nid says the bedroom mustiness and the kitchen's stale smell were gone, leaving air that simply smelled of nothing. Over the next weeks she kept bedroom humidity steady, washed bedding weekly and switched from a broom to a vacuum with fine filtration. Phum continued his prescribed medication and every follow-up appointment. Nid noticed he woke less at night, and she stopped seeing cockroaches in the kitchen.

The family's lesson: there is no single magic fix for post-flood allergies, but tackling every front in order, with ozone as the final step, made the house a place where everyone could breathe easily again.

Checklist: reducing dust mites and cockroaches after a flood

Control humidity first

• Open doors and windows on sunny days and use fans to push damp air outside.
• Run a dehumidifier or a cleaned air-conditioner in bedrooms to bring humidity down.
• Don't dry wet laundry in bedrooms; fix roof and pipe leaks.

Tackle dust mites

• Wash sheets, pillowcases and blankets weekly at around 60°C if the fabric allows.
• Use mite-proof covers on mattresses and pillows, especially for children and people with asthma.
• Cut back carpets, soft toys and heavy curtains in bedrooms; wash or box the toys you keep.
• Vacuum with fine filtration, with allergic family members out of the room.

Tackle cockroaches

• Throw out swollen wooden cabinets and wet cardboard boxes, their favourite hiding places.
• Seal cracks and gaps around pipes; fit floor-drain covers.
• Store food airtight, wash dishes promptly and take rubbish out daily.
• Use baits or professional pest control instead of fogging the whole house with spray.
• Wipe droppings and residue with a damp cloth or cleaner; never dry-sweep.

On ozone day

• All people, pets and plants must leave; move fish tanks out too.
• Seal opened food; open cupboards and drawers you want treated.
• Return only when the team confirms rest and ventilation are complete.

After treatment

• Air bedrooms further before an asthmatic child sleeps there.
• Make beds with freshly washed linen and keep humidity steady.
• Keep taking prescribed medication and attend follow-ups.
• Severe breathlessness, or high fever with calf pain, means hospital straight away.

Frequently asked questions

Does ozone kill dust mites?

Our service targets mould, bacteria, viruses and odour. Mites living deep in mattresses are best controlled by hot washing, mite-proof covers and lower humidity. Ozone finishes the job on mould and mustiness, a related group of allergy triggers.

Can ozone replace cockroach control?

No. Cockroach control requires sealing entry points, removing food and using baits or professional pest control. Ozone helps with the stale odour and bacteria in kitchen corners after cleaning.

Is ozone safe in a home with an asthmatic child?

Yes, when the procedure is followed: everyone out during treatment, and back only after rest and full ventilation. We suggest extra airing before the child sleeps in the room. A plus is that no chemical residue is left to irritate the airways.

Should ozone come before or after laundering and pest control?

After. Ozone works best as the final step in a home that is already clean and dry, and the results last longer.

The bedrooms didn't flood. Do they need treating?

In many homes, moisture from the ground floor rises upstairs, so bedrooms develop mould and mustiness without getting wet. The team will help assess which rooms to include.

Give your family air they can breathe deeply again

Free consultation and a step-by-step recovery plan for households with allergies and asthma.

Book Home Ozone Disinfection

Call 065-556-6294 · LINE @whd268 · worldhealthdisinfection@gmail.com

Promotion: ozone jobs from 15,000 baht receive a free medical-grade disinfectant spray.

Related services

• Residential and building ozone disinfection
• Ozone cleaning service
• Removing chemical residue with ozone
• Certificates and test results
• Contact us

References

• WHO fact sheets, including asthma and indoor air quality
• CDC: Floods – cleaning up and preventing mould after a flood