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Sunshine Helps Kill Germs Indoors

Analysis by Dr. Joseph Mercola Fact Checked

Story at-a-glance -

  • Research performed at the University of Oregon suggests letting sunlight in through your windows kills bacterial germs living in household dust
  • Compared to the amount found in dark rooms (12 percent), scientists discovered just 6.1 percent of the bacteria in household dust exposed to ultraviolet light remained viable
  • The average American spends about 93 percent of their time indoors, making them susceptible to the potential negative health effects associated with indoor toxins
  • Chemical toxins from flame retardants that leach from electronics and old furniture are known to accumulate in household dust, making it important to wipe down surfaces and vacuum regularly
  • Cleaning supplies and personal care products also contribute to the toxic load associated with indoor spaces

A new study from the University of Oregon suggests rooms exposed to sunlight contain less viable bacteria than those maintained in the dark. While more research is needed to fully understand how ultraviolet (UV) light changes household dust, I’ll take this opportunity to expose some of the toxins found in it.

Chemicals from flame retardants, household cleaners and personal care products accumulate in household dust and can potentially affect your well-being. Aside from implementing clean-air strategies in your home, another step you can take to avoid indoor dust and better your health is to spend more time outdoors.

Sunlight Shown to Reduce Dust-Dwelling Bacteria

Research performed at the University of Oregon (UO) suggests letting sunlight in through windows can kill bacteria living in household dust. The study, published in the journal Microbiome,1 quantified the dust-based bacteria that remained alive and viable when exposed to different lighting conditions. The scientists noted:2

  • Just 6 percent of bacteria exposed to UV light remained viable
  • 6.8 percent of bacteria exposed to daylight was viable
  • 12 percent of the bacteria found in dark rooms stayed viable

With respect to the context for this study, lead author Ashkaan Fahimipour, Ph.D., postdoctoral researcher at the UO's Biology and the Built Environment Center, said:3

"Humans spend most of their time indoors, where exposure to dust particles that carry a variety of bacteria, including pathogens that can make us sick, is unavoidable. Therefore, it is important to understand how features of the buildings we occupy influence dust ecosystems and how this could affect our health."

After analyzing the bacteria in household dust that had been seeded into miniature, climate-controlled rooms, where it was exposed to one of three types of lighting conditions for 90 days, the team discovered:4,5

  • Dust kept in the dark contained bacterial organisms that are closely related to types associated with respiratory illnesses; these organisms were largely absent in dust samples that had been exposed to sunlight
  • A smaller proportion of bacteria derived from human skin and a larger proportion of bacteria derived from outdoor air lived in dust exposed to light as compared to dust kept in the dark

Based on those findings, the researchers assert the presence of sunlight causes the indoor dust microbiome to more closely resemble bacterial communities commonly found outdoors. Says Fahimipour, "Our study supports a century-old folk wisdom, that daylight has the potential to kill microbes on dust particles, but we need more research to understand the underlying causes of shifts in the dust microbiome following light exposure.”6

Long Days Spent Indoors = Increased Exposure to Dust-Based Toxins

According to a survey sponsored by the U.S. Environmental Protection Agency (EPA), which gathered data from 9,386 respondents, Americans spend about 87 percent of their time in enclosed buildings and an additional 6 percent inside enclosed vehicles.7

That means most people spend just 7 percent of their lives breathing outdoor air. Spending this much time indoors each day puts you at risk for health problems associated with indoor air pollution. With respect to indoor air quality and illness, the EPA states:8

“Some health effects may show up shortly after a single exposure or repeated exposures to a pollutant. These include irritation of the eyes, nose and throat, headaches, dizziness and fatigue.

Such immediate effects are usually short-term and treatable. Sometimes the treatment is simply eliminating the person's exposure to the source of the pollution, if it can be identified.”

Some pollutants concentrate indoors, where levels may be two to five times higher than typical outdoor concentrations, the EPA says. 9,10 Though widely regarded as an aesthetic issue more than a potential health hazard, household dust has been identified as a major source of health-damaging pollutants.

The EPA notes those at increased risk of harm from indoor air pollution include the very young, older adults (especially the homebound) and those suffering from cardiovascular and respiratory diseases.11,12 In recent years, indoor concentrations of some pollutants have increased dramatically due to factors such as:13

  • Energy-efficient construction, which effectively seals buildings and homes in a manner that can reduce a structure’s breathability and hamper air exchange
  • Increased use of synthetic and toxin-laced building materials, furnishings, household cleaners, pesticides and personal care products

Household Dust Found to Contain 9,000 Species of Bacteria and Fungi

Your home, like your body, is filled with a vast array of microbes, many of which live in your household dust. In a 2015 analysis of dust from 1,200 U.S. homes, researchers discovered an average of more than 7,000 species of bacteria and 2,000 species of fungi.14,15

According to BBC News, among the fungi found in dust were well-known molds such as Aspergillus, Alternaria, Fusarium and Penicillium.16 The researchers noted the exact makeup of the fungal ecosystem hinged on the home’s location more than the design of the home and other factors. Study coauthor Noah Fierer, Ph.D., professor of ecology and evolutionary biology at the University of Colorado Boulder, said:

"Most of the fungi we are seeing in the home appears to be coming from outside … They enter the home on our clothing, or through open windows or … doors. Therefore, the best predictor of what types of fungi are in your home is where your home is located."17

The most intriguing aspect of the findings may have been the fact the microbial makeup of dust was strongly influenced by factors such as the sex of the occupants and the presence of pets. Fierer commented, "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."18

He added, "Bringing a dog or cat into your home really has a significant effect on the bacteria you find. …”19 While such high amounts of bacterial and fungal microbes may seem like a potential health danger, if you are in good health your immune system renders many of them harmless. The real danger indoors comes from chemicals and other pollutants that have been identified in household dust.

Dust in College Dorms Flagged as Potential Health Concern

Research published in the journal Environmental Science & Technology20 indicates dust in college dorms has the potential to damage human health. After collecting 95 dust samples from dormitory common areas and student rooms at two U.S. colleges, researchers detected 47 chemical flame retardants, many of which are believed to cause cancer and disrupt hormones.

Two flame retardants classified by the U.S. Environmental Protection Agency (EPA) as polybrominated diphenyl ethers, or PBDEs,21 were detected in the dorm dust at record levels:

  • Decabromodiphenyl ether, or DecaBDE: a flame retardant largely phased out in 2013, which the EPA has tagged as a “possible carcinogen” given its proven ability to cause cancer in lab animals
  • Pentabromodiphenyl ether, or PentaBDE: a chemical the EPA banned from manufacture in 2005, mainly because it is a known endocrine disruptor

The researchers noted the primary chemical within DecaBDE was found to be a shocking nine times higher than anything previously recorded. In addition, concentrations of PentaBDE were four times higher than levels found in any other environment.

Researchers suspect college dorms contain a higher level of flame retardants because they are small, somewhat-confined spaces containing a lot of electronics and, very often, old furniture and beddi ng, including pillows, some of which may contain flame retardants that have long since been banned.

The EPA says certain PBDEs, which are used as flame retardants in applications such as automobiles, plastics, textiles and wire insulation, have been shown to be “persistent, bioaccumulative and toxic to both humans and the environment.”22

Because PBDEs are not chemically bound to fabrics, foam, plastics or the other products in which they are used, they are more susceptible to leaching. Over time, as they leach, these chemical-laden particles from electronics and furniture settle into room dust.

Flame Retardants Are Believed to Damage Human Health

Of the four particular flame retardants found in 100 percent of the dust samples studied, three are suspected carcinogens. A chemical known as TCIPP or tris (1-chloro-2-propyl) phosphate was found in dorms at levels twice the median quantities found in other indoor environments.

While the effects of TCIPP require further study, chemicals similar in structure have been shown to have toxic effects on animal brain cells and are thought to decrease sperm counts and thyroid levels in humans.23 About the fourth chemical, named TPHP (triphenyl phosphate), the Environmental Working Group (EWG) states, “[T]here is growing evidence the chemical could affect hormones, metabolism, reproduction and development.”24

In a 2013 study,25 rats were exposed to the flame-retardant mixture Firemaster 550®, which is used in foam-based products and contains up to 20 percent TPHP. After discovering components of the chemical accumulated in tissues of rats — both before and after birth, resulting in obesity and early puberty for female rats — researchers now suspect TPHP may be a human endocrine disruptor.

Tips on Protecting Yourself From Flame Retardants

Lead dorm dust study author Robin Dodson, research scientist at the Massachusetts-based Silent Spring Institute, and Miriam Diamond, Ph.D., a professor in the department of earth sciences at the University of Toronto, offer the following advice on how to protect yourself from flame retardants:26

Avoid using older furniture in college dorm rooms, because the foam padding and other materials likely contain flame retardants

Inform your college student about the risks associated with flame retardants and encourage them to vacuum and wipe down surfaces on a regular basis to remove toxic dust

Ensure dorm rooms are well ventilated to avoid a buildup of leached chemicals

Wash your hands after touching cellphones, keyboards, laptops and tablets, most of which contain flame retardants

When replacing furniture and household items, choose products filled with cotton and wool, or even polyester, because they tend to be safer than chemical-treated foam

Look for items labeled as "flame-retardant free"

Be advised polyurethane foam products manufactured prior to 2005 — including foam used in mattresses, pillows and upholstered furniture — likely contain PBDEs. If you can, replace these items or, at a minimum, ensure the foam is in good repair and remains well-covered.

Because older carpet padding is another major source of PBDEs, take precautions when removing it. Before tearing out older carpeting, you'll want to isolate your work area from the rest of your house to avoid spreading PBDEs around. For best results when cleaning up carpet and pad debris, use a vacuum with a HEPA filter.

Cleaning and Personal Care Products Also Damage Indoor Air Quality

While doing your best to minimize leaching flame retardants, keep in mind the cleaning supplies you use also may be a source of toxins that affect indoor air quality. Unless you choose your cleaning products carefully, you may end up dousing your living space with even more toxic chemicals, many of which are not clearly identified on product labels.

Be advised so-called eco-friendly and green cleaners may still contain unsafe chemicals. Fortunately, concerns about the safety of cleaning and personal care products is growing nationwide. Increasingly more, government leaders and concerned citizens are pressuring manufacturers to disclose all ingredients used, as well as any toxic trace contaminants added during the manufacturing process.

One such chemical known as 1,4-dioxane, a probable carcinogen, has shown up in water supplies in Long Island, New York.27 Although 1,4-dioxane is primarily used as a solvent in manufacturing, it often ends up in cleaning and personal care products as a byproduct and has been detected in groundwater and drinking water.

During the manufacturing process for products like cosmetics, deodorant, shampoo and toothpaste, 1,4-dioxane develops through ethoxylation, a process that increases foaming and makes products less abrasive.28 According to the Citizens Campaign for the Environment (CCE), about 46 percent of personal care products — including body lotions, cosmetics, deodorants, detergents, dishwashing soaps and shampoos — contain 1,4-dioxane.29

“Once down the drain, the chemical is highly mobile in soil and does not easily break down, leading to contamination of groundwater-fed water sources,” asserts Harry Somma, the Long Island program coordinator for CCE.30

Unfortunately, because it is a manufacturing byproduct, 1,4-dioxane is not listed on ingredient labels, says the CCE, making it difficult for consumers to make informed and safe buying decisions about countless products they use daily.31

Act Now to Reduce Your Toxic Load and Get More Sunshine

While the amount of potentially toxic chemicals in your living environment may seem overwhelming, focus on the activities and areas over which you have some influence. Start by reading the labels on household cleaning products and stop buying the ones suspected to interfere with human health.

Better yet, as presented in the video above, choose natural alternatives or make your own nontoxic cleaning products. Wipe down surfaces regularly with soap and water and vacuum at least weekly using a HEPA filter to remove toxic dust.

When you are ready to replace bedding and furniture, get educated by reading customer reviews and manufacturer specifications. Choose organic, naturally flame-retardant materials and avoid items doused in toxic chemicals.

Finally, and perhaps most importantly, since sunshine has been shown to kill germs, I encourage you to spend more time outdoors. Also draw back your shades and open your windows for 10 to 15 minutes each day to improve indoor air quality and help “sanitize” your dust. Soaking up healthy amounts of sunshine is not only a great way to avoid the bacteria lurking in household dust, but it also gives you an opportunity to increase your vitamin D level naturally.