We know the skin is the largest human organ that fulfills many biological functions that are absolutely crucial for health and well-being (retainment of water, regulation of body temperature and protection from pathogens).
But, the clothes we wear can also be considered a kind of skin too: a second, artificial skin that protects us from environmental influences, such as cold, warmth, sunlight, rain, dirt, and injuries. And, as with our skin, our clothes can also become colonized (you might say contaminated!) with a diverse community of microorganisms. While it is undisputed that the human skin microbiota is largely beneficial for humans, the presence of microbes on clothes and other textiles is usually regarded as negative and unwanted.
Clothes, or textiles in general, offer quite good living conditions for microorganisms: a large surface, the capacity to store water, and a considerable amount of exploitable nutrients such as: dead skin cells, sweat, food residue, air-borne dust, and any other dirt collected during the day. Hence, it is not too surprising that microbes on clothes can sporadically reach densities similar to the maximum densities found on human skin, i.e. approximately 106 (1 million) per cm2.
Typically, a considerable variety of microbial species of human (skin, epithelia, gut) and environmental (water, soil, animals etc.) origin are found on clothes . Importantly, the availability of water is usually the key factor that controls microbial life on clothes and textiles; the dryer the fabric, the lower the microbial load and the possibility that microbes can proliferate.
Can microbes on my clothes make me ill?
With regard to the importance of domestic laundry hygiene, one of my former colleagues at Henkel used to say: “The most dangerous part [of clothes handling] is sorting the dirty laundry by hand before washing”.
Clearly, the infection risk associated with clothes or textiles is rather low, especially when compared to the risk associated with contact with hands and food, or gained from having direct contact with ill or infected human beings .
Usually, many of the microbes on your personal clothes are coming from your own body (in particular, from your skin) and can hardly make you ill. In addition, the amount of (pathogenic) microbes that your clothes gather during a normal day including (microbiologically unspectacular) activities, such as office work, public transport, shopping, homework etc., is probably very low, and not sufficient to cause infections. Finally, the route for a pathogenic microbe from your clothes into your body is not easy – particularly if you pay good attention to hand hygiene.
When it comes to working clothes (e.g. lab coats) or textiles (e.g. bedclothes, towels) used in hygienically challenging environments (clinics, medical practices, nursing homes, nursery schools, food production etc.), this is a different story. In these circumstances, where contact with infected and ill people or infectious material (blood, stool, meat) is very likely, clothes and textiles should be changed and cleaned appropriately on at least a daily basis.
Even under domestic conditions, some attention to the hygiene of clothes and textiles should be paid – not only to prevent the spread of infections, but also to prevent other unwanted microbial effects, such as malodor formation. Special attention should be given to all clothes and textiles that have direct contact with sweat, body fluids and skin (underwear, socks, towels, sportswear, bedclothes) or food and dirt (kitchen towels, cleaning tissues).
Nowadays, reusable face masks have to be counted among these items, too. Extra attention should be paid to regularly cleaning of textiles when household members are ill (e.g. with diarrhea), under homecare or suffer from any immune suppression. The clothes of people suffering from sensitive and/or skin diseases should be under special care, too, to prevent spreading diseases, such as athlete’s foot or warts, in their community.
How should I wash my clothes?
From a hygienic point of view, washing at a temperature of 60°C or higher with a bleach-containing heavy duty detergent and plenty of water for rinsing is the best and most effective strategy for disinfecting all clothes and textiles for which hygiene matters (see above). Doing so, the number of microbes on laundry is usually reduced by more than 5-6 log scales .
However, most sustainability-driven, modern washing trends (such as low-temperature washing or the use of bleach-free, liquid detergents, in combination with water) and/or energy saving programs mean higher temperatures are not the norm. Moreover, many fabrics (e.g. silk or modern sportswear) cannot be washed at higher temperatures without significant damage and are adversely affected by “aggressive” detergent components such as bleach.
Nevertheless, one should also keep in mind that inactivation and removal of microorganisms is only one aim of washing clothes. Removing stains and malodor are the others. And in the case of outerwear clothes worn only shortly, just a quick wash with a modern liquid detergent at a low temperature is absolutely sufficient.
In any case, laundry should be removed from the washing machine as soon as possible after the washing is finished and dried thoroughly before being stored away, either by using a dryer or outside in the sun – which has the added benefit of using the natural antimicrobial effects of UV light. Ironing also has an antimicrobial effect. On clean, dry laundry, microbes that might have survived the laundry process are unable to proliferate and cause, for instance, malodor.
Washing machine hygiene
Although designed to clean laundry, over time washing machines can themselves become significantly contaminated with microorganisms – in particular, with bacteria and molds. Washing machines are usually wet, warm and contain many parts that cannot be cleaned manually, as well as host a wealth of nutrients for microbes, e.g. the dirt that comes with the laundry (or even the laundry detergents themselves).
In a recent study , we identified 229 different bacterial species in different parts of the 13 domestic washing machines investigated. Microbial biofilms (thin films of bacteria adhered to each other and often a surface) in washing machines can cause corrosion, malodor and serve as a reservoir for (pathogenic) bacteria that recontaminate the laundry, especially during the final rinsing cycle. Notably, we detected particularly high proportions of Moraxella osloensis bacteria in the bulleye sealing of the washing machines. This bacterium is well known to cause the typical musty smell of textiles that have been “dried” and stored under humid conditions.
In order to prevent microbial contamination and smell from a washing machine, which in turn might cause laundry to stink, a few simple measures can be taken:
- From time to time use the “normal” instead of the “eco” washing programme, i.e. a higher washing temperature, and swap out a gentler detergent for a bleach-containing heavy-duty alternative
- Regularly clean all accessible parts of the machine (detergent drawer, sealings, sump) with soapy water
- After use, leave the door and detergent drawer open to let the machine dry out
- From time to time, clean the machine by letting it run without laundry at 90°C with a bleach-containing, heavy-duty detergent – special antimicrobial machine cleaners are not needed
Finally, a few microbes remaining on laundry after washing don´t have to be something bad.
Quite the contrary: A Swedish study  showed that in households, where the dishes are cleaned manually, instead of using a dishwasher, children were less affected by allergic diseases. Maybe due to a few more microbes remaining on the dishes, which might have an immune-stimulating effect? What if the same is true for laundry? It is not known if any study has ever addressed potential beneficial effects of microbes on clothes and textiles, but this should definitely be investigated in the future.
In summary, microbes on everyday clothes are nothing to really worry about, if you follow the advice given above. And maybe, some day we might not “wash” our clothes to simply remove adverse microbes, but also to specifically select for or impregnate it with microbes, that are beneficial for our (skin) health.
Want to know about how and when you should wash your hands? Read another article here by Dr Egert.
Key References: Bockmühl et al., 2019, Laundry and Textile Hygiene in Healthcare and Beyond. Microb Cell 6(7):299-306; doi: 10.15698/mic2019.07.682 Bloomfield et al., 2011, The infection risks associated with clothing and household linens in home and everyday life settings, and the role of laundry. Int Sci Forum Home Hyg(April): 1–43. Honisch et al., 2014, Impact of Wash Cycle Time, Temperature and Detergent Formulation on the Hygiene Effectiveness of Domestic Laundering. J Appl Microbiol 117(6):1787-97; doi: 10.1111/jam.12647 Jacksch et al., 2019, Influence of Sampling Site and other Environmental Factors on the Bacterial Community Composition of Domestic Washing Machines. Microorganisms, 8(1), 30; https://doi.org/10.3390/microorganisms8010030 Hesselmar et al., 2015, Allergy in Children in Hand Versus Machine Dishwashing. Pediatrics, peds.2014-2968; DOI: https://doi.org/10.1542/peds.2014-2968