Literature.

FindingDust samples were taken from 17 cars, 14 classrooms and 19 homes in Poland. In 23.5% of the cars, the cat allergen Fel d 1 was above 8 µg/g, and in 17.6%, the dog allergen Can f 1 was above 10 µg/g. The allergen was also found in the cars of drivers who don't keep pets.

What it meansFor allergens, the car is a second home. Allergen is carried from home to car on clothes and belongings, and builds up in the seats even if an animal has never been inside.

FindingIn Brazil, dust was collected from the fabric seats of 60 naturally ventilated buses, 60 air-conditioned buses and 60 taxis. Mite allergen was higher in the air-conditioned buses; in 82% of the samples from these buses, Der p 1 was at a sensitising level. Across all vehicles, more than 60% of samples had cat allergen at a sensitising level.

What it meansPublic transport seats are an allergen store that is constantly filling and emptying. Closed-loop air conditioning can increase mite allergen.

FindingIn the lab, bedding covers impregnated with Bacillus probiotics reduced the mite allergen Der p 1 in the fabric by 89%. In an 8-week trial with 20 patients allergic to mites, Der p 1 in mattress and pillow dust fell by a similar amount with both the probiotic and the placebo covers; those using the probiotic covers saw a clear improvement in rhinitis symptoms and quality of life.

What it meansA probiotic layer settled in the bed is promising for mite allergy, but it isn't a miracle on its own. That is why we say 'helps reduce' on this site.

FindingA protease enzyme called subtilisin, obtained from Bacillus species, was shown in the lab to break down the cat allergen Fel d 1, and was patented for reducing cat allergen in the environment.

What it meansCat allergen is a protein, and the enzymes Bacillus produces break down proteins. This is a laboratory finding, not a result measured in a home.

FindingTwo large studies in Germany examined dust from the homes of children growing up on farms. The more diverse the microbes in the home, the lower the children's risk of asthma.

What it meansA germ-free home isn't the goal. The diversity of the microbial community around a child is linked to how the immune system responds to allergens.

FindingIn France, sleep was assessed in 591 patients with allergic rhinitis using validated scales. Allergic rhinitis disturbed every aspect of sleep, and the worse the symptoms, the poorer the sleep quality.

What it meansSomeone with a blocked nose who sneezes through the night can't sleep deeply. Reducing the allergen load in the bed makes a difference to sleep too.

FindingTwo identical trains on the Milan metro were compared over 12 weeks. In one, chlorine disinfection was replaced with probiotic sanitation using Bacillus spores: wiped onto surfaces with a cloth and nebulised into the air. At the 4th measurement, the pathogen load in the air filters was 292,632 CFU/m² in the control train versus 74,526 CFU/m² in the probiotic train (−75%). On surfaces at week 12, it was 2,526 versus 0 CFU/m². The share of SARS-CoV-2 positive samples was 9.6% versus 3.7%. The train's overall bacterial community did not change significantly.

What it meansOne of the first controlled field studies in which probiotics were applied to the air. It wasn't done with Air Biotics; it shows the method itself.

FindingA review of probiotic sanitation on public transport. It notes that the Milan metro study is the only on-site study in this field so far and that more research is needed.

What it meansApplying probiotics to the air is a new field. The findings are promising, but the evidence is still limited.

FindingSummarises three ways probiotic cleaners work: competition for food and surface space (competitive exclusion); metabolites such as bacteriocins, biosurfactants and organic acids; and inhibition of biofilm formation. It notes that no virulence genes were found in the Bacillus strains used in the studies.

What it meansThe mechanism isn't just one thing: probiotics share the space and also make it harder for odour-causing microbes to take hold.

FindingA cleaner containing Bacillus spores inhibited the formation of S. aureus and E. coli dry biofilms on steel, ceramic and melamine surfaces by more than 97.7%.

What it meansProbiotics left on a surface make it harder for the biofilm that traps odour and dirt to establish itself.

FindingA cleaner containing spores of Bacillus subtilis, B. pumilus and B. megaterium was compared with conventional cleaning on hospital surfaces over 24 weeks. On surfaces cleaned with the spore-based cleaner, microorganisms associated with hospital infections stayed at lower levels.

What it meansSettling a harmless community onto a surface is a cleaning method in its own right. The idea itself has been tested in hospitals.

FindingWith spore-based Bacillus cleaning, the spores germinated on surfaces and took the place of pathogens; after one month, Bacillus made up about 70% of the surface microbiota, and pathogens were about 90% lower than with conventional cleaning. Probiotic cleaning did not select for drug-resistant strains, and an overall decrease in resistance genes was seen.

What it meansThe effect of probiotics builds up with regular use: settling onto a surface takes weeks. Unlike harsh disinfectants, it didn't make room for resistant species.

Finding6 hospitals in Italy, 18 months, 11,842 patients and 24,875 surface samples. After switching to a Bacillus spore-based cleaning system, the rate of hospital-acquired infections fell from 4.8% to 2.3%.

What it meansOne of the largest studies on probiotic cleaning. It was measured in hospitals; it isn't a direct claim for a household product.

FindingA critical review of 32 publications on microbial cleaners (15 of them hospital studies). It finds the results promising and argues that the methods need to be standardised and confirmed by independent studies.

What it meansThe subject isn't settled; research is ongoing. That is also why we give a source for every claim on this site.

FindingTrimethylamine-N-oxide (TMAO), found in the flesh of sea fish, is reduced to trimethylamine (TMA) by spoilage bacteria. The typical smell of spoiled fish comes largely from TMA.

What it meansThe fishy smell is a bacterial product. During cooking it is carried onto curtains and worktops with the oil vapour, and it doesn't go straight away when you air the room.

FindingAfter smoking, the nicotine and other compounds in the smoke cling to indoor surfaces such as walls, carpets, upholstery and dust, and over time get back into the air. This residue can linger in homes for a long time; researchers call it thirdhand smoke.

What it meansThe smell of stale smoke isn't in the air but inside fabrics and surfaces. Spraying perfume into the room doesn't touch this residue.

FindingNicotine stuck to surfaces reacted with nitrous acid in indoor air to form tobacco-specific nitrosamines. On cellulose surfaces, levels of these compounds rose tenfold after 3 hours of exposure.

What it meansCigarette residue keeps changing where it sits on a surface. That is why washing fabrics and cleaning surfaces matters.

FindingUrease, an enzyme produced by many species of bacteria, breaks urea down into ammonia and carbon dioxide.

What it meansThe sharp smell of cat litter comes from bacteria turning the urea in urine left in the litter into ammonia.

FindingThe main component of foot odour is isovaleric acid. Staphylococcus epidermidis, found naturally on the skin, produces this acid by breaking down the amino acid leucine in sweat.

What it meansSweat has no smell; the odour is made by bacteria that feed on sweat. That is why shoes and gym bags keep on smelling by themselves.

FindingMould and bacteria release volatile organic compounds (MVOCs) as part of their metabolism. The review looks at 96 typical MVOCs and the 15 most often measured in damp-damaged buildings; the most notable effect is irritation of the eyes and upper airways.

What it meansThe musty smell of damp is made up of compounds released into the air by microorganisms growing on damp surfaces. If there's a smell, something is growing.

FindingOn average, the mould load in air conditioner filters was about 5 times that of carpets; Cladosporium and Penicillium were dominant. With the air conditioner running, mould spores in the room air were about twice the level of rooms without air conditioning, and the highest level was measured when the air conditioner was first switched on.

What it meansThe sour smell when you turn on the air con comes from a filter kept wet by water condensing in the indoor unit. The filter needs to be cleaned and dried.

Finding25 fragranced products, including air fresheners, cleaning and laundry products, were measured giving off 133 different volatile organic compounds, an average of 17 per product. 24 of them were classed as toxic or hazardous under US law. Of the 133 compounds, only ethanol was listed on any label. Emissions from products labelled 'green' were not clearly different from the others.

What it meansThe scent of a room spray isn't a single substance but a mixture of dozens of compounds. Often the label just says 'perfume'.

FindingIn a survey of 1,136 adults representative of the US, 34.7% of participants reported health problems such as migraines and breathing difficulties when exposed to fragranced products. 20.2% said that if they entered a workplace sprayed with air freshener, they left as quickly as possible.

What it meansA scent one person finds pleasant can be a headache for someone else in the same room. An unscented product is safer common ground for everyone.

FindingTerpenes in cleaning products and air fresheners can react quickly with ozone in indoor air to form secondary pollutants such as formaldehyde.

What it meansHeavy perfume is a chemical load added to the air, and it keeps changing once it's there. Rather than masking a smell, you need to reduce its source.

FindingMore than 3,500 adults in 10 countries were followed. Among those who used cleaning sprays at least 4 days a week, the risk of doctor-diagnosed asthma was 2.11 times higher. The risk was greatest with glass, furniture and air freshener sprays.

What it meansWith products used as sprays, the ingredients matter even more, because the droplets are breathed in directly.