A standard washing machine reduces most bacteria and many viruses, but it doesn’t reliably kill all of them. A typical cold-water cycle with detergent removes 92 to 99% of common germs from fabric, which sounds impressive until you consider that millions of organisms can remain on heavily soiled items. Whether your laundry comes out truly sanitized depends on three factors working together: water temperature, detergent chemistry, and drying.
What Detergent Actually Does to Germs
Laundry detergent plays a dual role. First, it physically lifts bacteria and viruses off fabric fibers so they can be flushed away with rinse water. Second, the surfactants in detergent directly damage certain types of pathogens. Enveloped viruses, the category that includes flu and the virus that causes COVID-19, are surrounded by a fatty membrane. Surfactants dissolve that membrane, essentially bursting or perforating the virus and rendering it unable to infect cells. This is the same basic principle behind handwashing with soap.
Non-enveloped viruses are a different story. Pathogens like norovirus, rotavirus, and hepatitis A lack that vulnerable outer membrane, which makes them far more resistant to detergent alone. In lab tests, washing contaminated fabric swatches with detergent reduced rotavirus and hepatitis A by roughly 99%, but enough virus survived to still pose an infection risk, particularly when you transfer wet laundry to the dryer with bare hands.
How Much Water Temperature Matters
The median cold-water wash in U.S. households runs at about 14°C (58°F). At that temperature, you’re relying almost entirely on detergent and mechanical agitation to remove germs, not heat. Bacteria like Staphylococcus aureus have been shown to survive wash programs at 50°C (122°F), and most home hot water heaters are capped at 49 to 52°C (120 to 125°F) to prevent scalding. So even a “hot” cycle in a residential machine often falls short of the temperatures needed to kill hardier organisms.
The thresholds that matter for serious pathogens are higher. SARS-CoV-2 requires 60°C (140°F) sustained for 20 minutes, or 65°C (149°F) for 5 minutes, to achieve a meaningful kill rate. Enveloped viruses can be inactivated at temperatures as low as 20°C when combined with an oxygen-based sanitizing detergent, but tougher pathogens like enteric viruses and certain fungi may need hot water plus chlorine bleach to reach targeted reductions.
That said, one older but well-cited study found that cold-water wash formulas (around 31°C) combined with a bleach cycle reduced bacterial counts by the same amount as hot-water washes: a roughly 1,000-fold reduction. The takeaway is that temperature alone isn’t the deciding factor. The combination of temperature, detergent, and any added sanitizer matters more than any single element.
Your Washing Machine May Add Germs, Too
Here’s something most people don’t consider: your washing machine harbors its own bacterial ecosystem. Research published in Frontiers in Microbiology found that the number of living bacteria in water coming out of a washing machine was generally no lower than the number going in. That’s because bacteria build up biofilms on internal components like the rubber door gasket, detergent drawer, and drum. These biofilms harbor potential pathogens including Pseudomonas and Klebsiella species, sometimes at higher levels than those found on household toilets.
In one experiment, brand-new, unused cotton fabric came out of a low-temperature wash cycle colonized with a diverse mix of skin, textile, and machine-related bacteria. The laundering process essentially shuffled microbes between the clothes, the water, and the machine itself. This means your washing machine can transfer bacteria from one family member’s clothing to another’s, and it can spread odor-causing species across loads. Lower wash temperatures make this cross-contamination more likely because fewer organisms die during the cycle.
The Dryer Finishes the Job
Drying provides a significant second wave of germ killing that washing alone often can’t accomplish. The CDC notes that temperatures reached during machine drying (and ironing) provide “additional significant microbiocidal action” regardless of whether hot or cold water was used in the wash. A standard dryer cycle at its high setting, around 57 to 70°C (135 to 158°F) for most residential machines, adds roughly another 0.5 to 1.0 log reduction in bacterial counts on top of what washing achieved. That translates to killing an additional 70 to 90% of whatever survived the wash.
For everyday laundry, running the dryer on a high heat setting and ensuring clothes are fully dry before folding provides a meaningful layer of protection. For items that can’t go in the dryer, drying in direct sunlight offers some UV-based antimicrobial benefit, though it’s less reliable than heat.
When You Need More Than a Normal Wash
For routine laundry from a healthy household, a standard detergent wash followed by thorough drying handles the job adequately. But certain situations call for extra measures.
- Stomach bugs (norovirus, rotavirus): Detergent alone leaves enough virus on fabric to cause infection. Use the hottest water the care label allows and add chlorine bleach for whites or an oxygen-based bleach for colors. Wash your hands after handling contaminated laundry.
- Illness in the household: Wash sick family members’ clothing and bedding separately. Use the hottest appropriate water temperature and the highest dryer heat setting. Don’t let wet, contaminated laundry sit in the machine.
- Immunocompromised family members: Consider a laundry sanitizer product. Lab testing shows that sanitizers containing quaternary ammonium compounds or PCMX (the active ingredient in some antibacterial products) completely inactivated SARS-CoV-2 within 15 minutes at room temperature. These products are designed for use in the pre-soak or wash cycle at cold temperatures.
Some newer washing machines include a dedicated sanitize cycle. Machines certified under NSF Protocol P172 must demonstrate that their sanitize cycle reduces 99.9% of microorganisms. If your machine has this setting, it’s your most reliable option for germ elimination without additives, though it uses more energy and may not be suitable for delicate fabrics.
Keeping Your Machine Clean
Because biofilms accumulate inside washing machines over time, periodic cleaning helps limit cross-contamination. Running an empty cycle on the hottest setting with bleach or a machine-cleaning product once a month breaks down bacterial buildup. Leaving the door or lid open between loads allows the drum and gasket to dry, which discourages microbial growth. Wiping the rubber door seal on front-loaders is especially important, since trapped moisture there creates an ideal environment for bacteria and mold.