Image copyright Science Photo Library Image caption The house dust contained 2,000 types of fungi - including Aspergillus shown here 
 
 The dust in our homes contains an average of 9,000 different species of microbes, a study suggests. 
 
 Researchers from the University of Colorado at Boulder analysed the dust found in 1,200 households across the United States. 
 
 They discovered that the types of bacteria and fungi varied depending on where the home was located, who lived there and whether pets were present. 
 
 The research is published in the Proceedings of the Royal Society B. 
 
 This is really basic natural history we are investigating here Dr Noah Fierer, University of Colorado at Boulder 
 
 Dr Noah Fierer, associate professor of ecology and evolutionary biology, who carried out the study, said: "This is really basic natural history we are investigating here. 
 
 "We have known for a long time that microbes live in our homes. What we are doing is now is old-fashioned science, to see how they vary across space." 
 
 The study is part of a citizen science project called The Wild Life of Our Homes. 
 
 Image copyright Anne Madden/Robin Hacker-Cary Image caption The scientists were sent house dust samples from 1,200 homes across the United States 
 
 Volunteers from 1,200 homes across the United States sent dust samples to the researchers. 
 
 They scooped up the detritus from the ledges above doorways - a spot, the scientists say, that is often overlooked while cleaning. 
 
 A genetic analysis of the house dust revealed a menagerie of microscopic creatures. 
 
 The researchers found that the average household had more than 2,000 different types of fungi. 
 
 These included well-known moulds such as Aspergillus, Penicillium, Alternaria and Fusarium. 
 
 However, the exact make-up of the fungal ecosystem depended on the home's location. 
 
 "Most of the fungi we are seeing in the home appears to be coming from outside the home," said Dr Fierer. 
 
 "They enter the home on our clothing, or through open windows or through doors. 
 
 "Therefore the best predictor of what types of fungi are in your home is where your home is located." 
 
 Image copyright Science Photo Library Image caption Staphylococcus was among the 7,000 different types of bacteria found 
 
 The researchers also discovered an average of 7,000 different types of bacteria per household. 
 
 Some, such as Staphylococcus and Streptococcus, were commonly associated with human skin. 
 
 People do not need to worry about microbes in their home Dr Noah Fierer, University of Colorado at Boulder 
 
 However others, such as Bacteroides and Faecalibacterium, were linked to faeces. 
 
 But here, the species varied according to who - or what - was living in the house. 
 
 "We found distinct bacteria in homes that had women and homes that were male-only," said Dr Fierer. 
 
 "There are some kinds of bacteria that are more common on women's bodies than on men's, and we can see the impact of that on the bacteria found in house dust." 
 
 Pets also added to the microbe mix. 
 
 "Bringing a dog or cat into your home really has a significant effect on the bacteria you find in your home," explained Dr Fierer. 
 
 "It was surprising to us that it was such a strong influence - stronger than any other factor, stronger than where your home was located or the design of your home, for example." 
 
 While the study was carried out in the United States, Dr Fierer said that the findings would be relevant for other parts of the world. 
 
 Image copyright Anne Madden/Robin Hacker-Cary Image caption The researchers wanted to see how microbes varied across different households 
 
 The researchers now want to find out how sharing our homes with these organisms could affect human health. 
 
 While some microbes may be linked to disease and allergies, they say most are probably harmless - and some may even be beneficial. 
 
 Dr Fierer added: "People do not need to worry about microbes in their home. They are all around us, they are on our skin, they're all around our home - and most of these are completely harmless. 
 
 "It is just a fact of life that we are surrounded by these microbes." 
 
 Follow Rebecca on Twitter. ||||| A new analysis of more than two dozen studies found toxic chemicals in 90 percent of household dust samples taken from 14 states. 
 
 Household dust does more than collect in corners and on bookshelves full of novels you haven’t gotten around to reading. A new study shows it can expose people to a wide range of potentially toxic chemicals. 
 
 In what the authors are calling the first study of its kind – a meta-analysis of more than two dozen previous studies on chemicals in dust – they report that 90 percent of dust samples taken from houses in 14 states contain harmful chemicals, including one that’s known to cause cancer. 
 
 “Most studies only measure a few chemicals so it makes it hard to understand typical exposures in homes and work places,” said the study’s lead author Ami Zota, an assistant professor of environment and occupational health at Milken Institute School of Public Health at the George Washington University, in Washington, D.C. 
 
 The researchers – who also came from Harvard University, the University of California-San Francisco, Silent Spring Institute and the Natural Resources Defense Council – analyzed data from 26 peer-reviewed papers and one unpublished set of data. The collected data included 45 chemicals from five chemical classes. 
 
 “We wanted to be able to draw more solid conclusions about concentrations of indoor chemicals in the U.S. by pooling data across all of these studies,” Zota explained. 
 
 The chemicals studied come from all sorts of common consumer goods, including furniture, personal hygiene products, flooring, baby products, cleaning supplies, fast food and food packaging. Zota said the chemicals are released into the air and then seep into dust that settles on furniture and floors. People can inhale or ingest small particles of dust or even absorb them through the skin. 
 
 To analyze the previous studies, the scientists parsed the information from three different angles: the level of chemical concentration in dust, how much might be getting into our bodies, and how hazardous the chemicals are. 
 
 “No matter which way we looked at it, there were some chemicals that stood out,” co-author Veena Singla, a staff scientist with the Natural Resources Defense Council, told CBS News. The non-profit group helped to fund the study. 
 
 Ten harmful chemicals were found in 90 percent of the dust samples tested. Phthalates, used in toys and vinyl flooring, among other products, occurred in the highest concentrations. 
 
 They were followed by phenols, often used in cleaning products. Then came flame retardants, fragrances and perflouroalkyl substances, which are used in carpets, textiles, and leather to make them water-, oil- and stain-repellent and to create grease-proof and waterproof coatings for products such as paper plates and food packaging. 
 
 “Phthalates are linked to multiple health hazards, including reproductive,” Signla said. “And some flame retardants are linked to cancer.” 
 
 The authors of the study, published in the journal Environmental Science & Technology, were especially concerned about exposure to children, especially very young children who crawl around on the floor and put their hands in their mouths. 
 
 Chemicals of top concern: 
 
 TCEP - A flame retardant added to couches, baby products, electronics and other products 
 
 DEP, DEHP, BBzP and DnBP – These chemicals, different varieties of phthalates, are found in an array of drugstore items like those listed above, as well as some highly processed foods and fast food. Phthalates are also linked to IQ and respiratory problems in children. 
 
 PFOA and PFOS - These chemicals​ are found in cellphones, pizza boxes and many non-stick, waterproof and stain-resistant products. They’ve been linked to developmental problems​ and issues with the immune, digestive, and endocrine systems. 
 
 These may be worrisome when they accumulate in household dust, the researchers say. 
 
 “Indoor dust is a reservoir for commercial consumer product chemicals and many of these chemicals have known and suspected health effects,” Zota said. 
 
 “This is the first study where we can get a more comprehensive picture of chemical contamination in the home,” Singla added. “Previous studies were like looking at the individual dots in an Impressionist painting. Putting this data altogether, we could see what the bigger picture is and it’s really kind of scary.” 
 
 The authors said small amounts can add up over time and potentially impact health. 
 
 “On the one hand, I wasn’t that surprised, and on the other hand I was surprised to see just how bad it was. I definitely expected to see a number of toxic chemicals when we put the data together, but just the extent of it did surprise me,” Singla said. 
 
 The study doesn’t answer all of the researchers’ questions, however. There are still big gaps in knowledge about many chemicals. 
 
 “We know so little about fragrance chemicals. They’re a prime example of the problem of not having information on what’s in our products because companies claim trade secrets,” Singla said. 
 
 Safer alternatives need to be developed, said Zota. 
 
 “One of our objectives with this – because there are so many consumer product chemicals being used currently in commerce with incomplete health and safety information – was to conduct this analysis with the objective of helping researchers as well as decision-makers to set priorities. Which chemicals to prioritize, in terms of conducting future health assessments. As well as which chemicals to actively develop safer alternatives for,” Zota said. 
 
 Individuals can take a number of steps to improve safety, Singla said. 
 
 In your own home, day-to-day, washing your hands​​ with plain soap and water can cut down on the amount of dust you come into contact with. Vacuuming with a HEPA-filter, wet mopping and dusting with a damp cloth can reduce exposure to dust, as well. 
 
 In the longer term, she said, “There are regulatory and legislative solutions. It does make a difference when people tell their government agencies that this matters to them and they’re concerned.” Singla also noted that the Natural Resources Defense Council has a petition for the FDA to ban phthalates from food, which supporters can sign online. 
 
 “We think our homes are safe havens, but what we found is the surprising reality that our homes are being polluted by the products we have every day. Our choices about what we buy and the policies we support can make a real difference,” Singla said.
– Last year, volunteers mailed in dust samples taken from above interior and exterior door frames in 1,200 homes across the US as part of a citizen science project called Wild Life of Our Homes. Now, scientists are reporting in the journal Proceedings of the Royal Society B that our dust reveals a lot about who we are and where we live. There are 9,000 unique species of microbes in our dust, reports the BBC, with an average of 7,000 of those being bacterial. There are also insect parts, pollen, dead animal cells, dry wall powder, carpet fibers, and soil particles. "I don't want any readers to be paranoid about this," Noah Fierer, a microbial ecologist at the University of Colorado at Boulder, tells the Los Angeles Times. "Most of the organisms are completely innocuous, and some may be beneficial." The No. 1 thing researchers can now predict about a home based on a simple analysis of dust? Whether cats or dogs live there. The type of fungi tends to be indicative of a home's geographical location, but bacteria change depending on who lives there—and that doesn't just mean what types of pets, but even whether a home is inhabited primarily by men or women. "There are some kinds of bacteria that are more common on women's bodies than on men's, and we can see the impact of that on the bacteria found in house dust," says Fierer. And while most of the fungi and bacteria are likely harmless, some could be linked to diseases and allergies, something scientists want to study further to discern how our dust specifically affects our health. (Did you know there's more dust in the world now than ever?)