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Airing Dirty Laundry Issues

A 1999 University of Arizona study found 25% of home washing machines were contaminated with fecal bacteria. Several factors were implicated in contributing to the contamination of the washers.

Dr. Charles Gerba, the author of the laundry study, maintains our laundry is becoming less clean. He determined this by sampling 100 four-person households in the Tuscon, AZ and Tampa, FL areas. Dr. Gerba and his associates washed sterile washcloths in these machines and took samples from under their rims.


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While most people can hazard a guess as to the source of the fecal matter, Dr. Gerba gives us a precise measurement in the offending garment. Each pair of worn underwear awaiting laundering “contains about one-tenth of a gram of bacteria-carrying feces, which equals about one quarter of a peanut,” he says. While 25 percent of the washing machines were contaminated with fecal matter, the E. Coli strains themselves weren’t harmful. However, they indicate the possibility of the presence of other disease-causing organisms.


Five Factors to Help Ensure Clean Laundry

  1. Time – Laundry detergents need time to do their work in the laundry cycle.
  2. Temperature – Unless specifically designed for cold water washing, laundry detergents optimally require water temperatures above 140 degrees F. Removal of soils may be reduced at lower temperatures.
  3. Mechanical Action – Water levels need to be adequate for the mechanical action of the washer to enable laundry detergent to properly clean clothes. Flow is needed for ample flushing and rinsing, which is vital for removal of free-floating, water-soluble soils.
  4. Laundry Procedures – Loading the proper amount of clothing in the washer and minimizing the time elapsed between washing and drying clothes are important laundering factors.
  5. Laundry Detergents and Chemicals – Unless stated otherwise on the label, most powders require warm to hot water to dissolve properly. They will dissolve in cold water but not necessarily quickly enough to be effective. Liquid detergents do become active in a very short time regardless of water temperature. Read and follow the label.

 “Detergent and water remove 99 percent of the organisms, but when you start out with 100 million of them, you’ve still got a million left,” Dr. Gerba points out. So why does Dr. Gerba think our laundry is becoming less clean?

  • Wash cycles and drying cycles are shorter (they now average 20 minutes and 28 minutes respectively).
  • To save money and electricity, fewer Americans wash clothes in hot water, and even fewer use bleach due to the many types of fabrics being laundered in home washers today.
  • Mechanical action and proper rinsing away of soil and microbes can be lost when machines are overloaded. Overloading inhibits flow of water through fabrics for dispersal of detergent, flushing and rinsing. Even if not overloaded, however, the microbes from one wash load stay in the washer and can be transferred to the next load.
  • Many people are unaware their home laundry procedures should include disinfecting surfaces that come in contact with dirty laundry and wet laundry, including laundry hampers and hands. In addition, leaving wet laundry in the washer after the washing cycle for hours creates a prime breeding ground for bacterial growth.
  • Many people wash in cold water regardless of the type of laundry detergent used, instead of following directions on laundry detergent labels and washing in the appropriate temperature recommended by the manufacturer.

But won’t the heat of the dryer kill microbes contaminating the laundry? In Dr. Gerba’s study, some microbes on the wet wash were found to survive even the heat of the permanent-press drying cycle – including Salmonella, Hepatitis A, rotavirus and adenovirus – so you can’t count on the dryer to kill the bacteria and viruses.


How do we cure this microbial invasion of our laundry? Dr. Gerba recommends the following:

  • Wash undergarments with one cup of bleach added to the wash water, or
  • Before or after washing clothes, run one wash cycle with only bleach and water to disinfect your washing machine, and wash underwear in the last load.
  • Wash clothes at a temperature of 140 degrees or higher (difficult for most household washing machines).
  • Use protective gloves when transferring wet clothes from the washer to the dryer, or wash your hands immediately afterwards.
  • Use a detergent that contains a sanitizer.

The laundry detergent industry knows consumers want to wash clothes in cold water to save energy and money, and they also want bacteria-free clothes. Several new “sanitizing detergents” which contain bleach but are effective in cold water are now on the market. While regular detergent killed most but not all of the three bacteria strains (including E. Coli) tested at all three temperatures, the sanitizing detergents killed all three types, even in cold water.


While it hasn’t been proven that bacteria on clothes spread illness, if someone in your family is sick or you are washing loads of underwear, using a sanitizing detergent may be a smart choice.


Breckenridge, M. B. (2000, November 22). Clean Up to Avoid Spread of Germs. Knight Ridder/Tribune News Service .
Manning, A. (1999, June 27). Finding Germs Where You Least Expect Them. Chicago Sun Times.
Mitchell, J. (2002, February 1). Spotting (and Solving) Laundry Problems. Nursing Homes .
Mr. Clean: Professor Lifts the Lid on Household Germs. (1999, March 1). The Milwaukee Journal Sentinel.
What's Lurking in Your Laundry. (2000, June 1). Good Housekeeping.

Airing Dirty Laundry Issues:  Created on June 4th, 2009.  Last Modified on January 21st, 2014


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About Janice Stewart

Janice Stewart has a Bachelor of Science degree in Nutrition from James Madison University and a MS in Nutrition Science from Rutgers University. She practiced as a Registered Dietitian for 20 years in hospitals, nursing homes and home health agencies in North and South Carolina. She has also attained specialty certifications as Certified Nutrition Support Dietitian and Certified Diabetes Educator, and still retains her status as a Registered Dietitian.

Janice has applied her biochemistry background and hospital experience to develop and implement cleaning processes that take cleaning beyond aesthetics to improve health and quality of life. Janice is vice president and owner of Castle Keepers, a residential cleaning company based in Charleston SC.