Towels and Bacteria: The Real Problem Starts Much Earlier

New data suggests that the real issue starts much earlier.

In the bathroom, everything can appear clean as long as there is no unpleasant smell or visible dirt. Hand towels and bath towels in particular tend to fall into this category: soft, freshly laundered and seemingly harmless. However, a Japanese study paints a very different picture, showing when an invisible bacterial colony becomes established in the fabric.

When a soft towel becomes a bacterial breeding ground

A research group led by microbiologist Kato closely examined bath towels in 26 Japanese households over six months. From October 2021 to March 2022, they assessed hand towels and shower towels used normally in everyday life. At regular intervals, the team analysed the microbial load within the textile fibres.

Their findings were clear: every use adds to the number of germs. Skin bacteria, sweat, flakes of skin, minute traces of soap, cosmetics and dirt gradually build up within the fabric's structure. Bathroom conditions are particularly favourable for this process, as they are warm, humid and often poorly ventilated.

The researchers identified a distinct tipping point at around eight weeks after first use. From then on, microorganisms start to form what are known as biofilms: complex communities that become firmly embedded in the fibres.

“After around two months, a seemingly clean terry towel becomes a stable bacterial refuge that is difficult to remove.”

164,000 bacteria per square centimetre in an everyday towel

The recorded figures are striking. After roughly two months of regular use, towels in the study reached loads of up to 164,000 bacteria per square centimetre. Human skin naturally hosts many microorganisms too, but a towel offers especially favourable conditions for growth because it provides both moisture and nutrients.

The more worrying issue is not simply the overall quantity, but the types of germs involved. The study repeatedly refers to faecal coliforms: bacteria originating in the gut, including Escherichia coli. They can reach a towel via inadequately washed hands and then spread further from there.

Comparable research has found that, in individual samples, up to 90 per cent of analysed towels showed traces of faecal contamination. The areas used to dry hands and faces were especially affected.

Earlier measurements by environmental microbiologist Charles Gerba also demonstrated how rapidly germs can multiply. After just three uses without washing, bacterial levels rise sharply. Anyone using the same towel for several consecutive days is therefore creating ideal starting conditions for a small bacterial farm.

Biofilm in towels: when bacteria form a protective shield

Biofilm may sound like an abstract term, but it describes a very tangible process. Bacteria attach to a surface in groups, produce a slimy matrix and use it as protection from external influences. It is familiar from dental plaque and deposits in shower drains - and it can also develop in older towels.

“Once it has formed, the biofilm acts like armour: detergent and moderate washing temperatures can barely reach the bacteria.”

According to the Japanese investigation, several factors contribute to this development:

• Persistent dampness: Towels often do not dry completely between showers.
• Bathroom warmth: Heating, hot showers and limited air circulation speed up bacterial growth.
• Organic material: Skin flakes, sweat and soap residue provide nutrients.
• Shared use: When several people use the same towel, the diversity of germs increases.

After around 60 days of use, the biofilm becomes so stable that ordinary household washes at 40°C are often no longer sufficient to significantly reduce the bacterial colonies. The researchers say the towels are effectively “rebuilt” at this stage, as the microbial ecosystem within the fabric has changed permanently.

How often should towels really be washed?

The observations point to a fairly straightforward rule of thumb: hand towels and shower towels should ideally be washed every two to three days. This keeps bacterial numbers comparatively low and usually prevents a stable biofilm from becoming established in the first place.

A wash at at least 60°C is recommended, with a sufficiently long cycle and a heavy-duty detergent containing bleach. Washing at only 40°C will reduce germ levels as well, but it does not have the same effect on resistant bacterial communities.

The drying process matters just as much. A towel left damp and bunched up on the floor for hours, or hanging over a radiator, remains an ideal environment for germs.

How to keep towels more hygienic

A few simple habits can considerably reduce the risk:

• Spread towels out fully after use rather than hanging them up folded.
• Provide separate towels for every member of the household, particularly for faces and hands.
• Let textiles dry quickly and thoroughly in well-ventilated rooms or outdoors.
• Replace visibly worn or rough towels after extended use, and at the latest when they still smell musty despite washing.
• Increase washing frequency substantially when someone in the household is ill with a stomach bug or cold.

When replacing a towel is the better option

The Japanese data indicates that biofilms formed after around 60 days of intensive use are difficult to remove fully. Anyone who has used their favourite towel continuously for months and washes it only rarely is therefore likely to be carrying around a well-established reservoir of germs.

In practical terms, this does not mean throwing away every towel after two months. What matters is how intensively and frequently it is used, how hot it is washed and how quickly it dries. If a shower towel is used daily, washed only every ten days and dried in a poorly ventilated bathroom, it is worth taking a critical look - and replacing it if in doubt.

“If a towel still smells slightly musty after a fresh wash, that usually signals that the biofilms are sitting deeper in the fabric than the washing machine can reach.”

What lies behind the ‘good’ and ‘bad’ bacteria?

For many people, bacteria automatically sound dangerous, yet most are harmless or even beneficial. Our skin is home to a complex microbiome that protects us and helps keep pathogens at bay. A towel, however, can contain a wide range of species, including some that have little business being there.

The study identified aquatic bacteria such as Aureimonas and Brevundimonas, which would normally be expected in water rather than on textiles. In a damp bath towel, though, they apparently find ideal conditions and gradually alter the microbial composition of the material.

There are also germs from the environment, the bathroom, pets and, naturally, the human body. The more sources that come together, and the longer a textile stays in use, the more varied and unpredictable this mixture becomes.

Specific risks - and who should be particularly careful

For healthy people with a robust immune system, contact with lightly contaminated towels will usually have no consequences. Even so, there is an increased risk of:

• Skin irritation and minor inflammation
• Spots or worsening facial acne caused by contaminated face towels
• Transmission of diarrhoeal pathogens via contaminated hand towels or guest towels

Certain groups are particularly sensitive:

• Babies and young children with delicate skin
• People with eczema, atopic dermatitis or broken skin
• Older people and those with weakened immune systems

In these cases, it is worthwhile taking a much stricter approach to towel hygiene, using individual towels and washing them more frequently.

Better hygiene through simple everyday habits

Small adjustments to a bathroom routine can reduce the germ load without much effort. An extra hook for a face towel, a second set of towels in the cupboard and regular ventilation after showering can all help stop biofilms gaining a stable foothold.

Perhaps the most important point is to move away from the habit of changing a towel only once it looks visibly dirty. Bacteria cannot be seen, and they often cannot be smelled until the problem is already well advanced. The Japanese study offers a clear prompt to reconsider this - with a simple consequence: change towels more often, wash them hotter and retire heavily used old towels in good time.