Hand Dryers: Viral Laboratory Experiment Raises Germ Concerns

A viral laboratory experiment now suggests that these appliances could have the opposite effect.

More and more washrooms are doing away with paper towels in favour of electric hand dryers. Environmentally friendly, touch-free and modern: that is the promise. A UK scientist tested the machines in a laboratory. Her findings have since left many users feeling uneasy as they stand in front of the airflow.

How a simple experiment reframes the question of germs

The researcher, who is active online under the name “Devon Science”, wanted to find out what the hot or cold blasts from hand dryers are actually blowing onto our skin. Rather than setting up a high-tech test, she used a straightforward, traditional tool: Petri dishes containing growth medium.

She placed one dish directly beneath the air outlet of a hand dryer in a public toilet. A second dish was left in the laboratory as a control sample, providing a comparison with clean indoor air.

After one day in an incubator, the contrast was stark. The control dish remained almost clear, while the dish from the toilet was covered in yellow, black and white spots.

The Petri dish from the hand-dryer area was teeming with bacterial colonies compared with the almost empty control sample.

The experiment indicates that the appliances stir up micro-organisms from the washroom air and blow them in a concentrated stream onto freshly washed hands.

Which germs appear in the hand dryer airflow

The colonies grown during the experiment can broadly be divided into several groups, including well-known potentially harmful germs:

• Staphylococcus aureus: Often found on the skin and in the nose, it can cause inflammation or abscesses in minor wounds and, in extreme cases, blood poisoning.
• Escherichia coli (E. coli): A typical gut bacterium found in faeces. In toilet areas, it can easily settle on surfaces and then be carried elsewhere.
• Fungal spores: Black spots point to fungi. They can irritate the respiratory tract and affect people with allergies or weakened immune systems.

This means the airflow may contain more than harmless environmental flora: it can include a mixture of potential pathogens that is difficult to control, particularly in heavily used toilet facilities.

Why hand dryers spread germs so effectively

The key issue is not simply that air is moved, but the force with which it is propelled and the way the machines are designed.

High air speed turns hand dryers into germ catapults

Modern jet dryers can reach air speeds reminiscent of a storm. Manufacturers cite speeds of up to 400 miles per hour, meaning well over 600 kilometres per hour in the air stream.

This has two consequences:

• Water droplets and germs can be dislodged from every corner of the washroom and propelled into the air.
• Anything that has previously settled on the floor, walls or the appliance housing may be stirred up again.

Anyone holding their hands directly beneath this stream is, in effect, standing at the centre of a microbial wind machine.

Dirt inside the appliance

For the second stage of her test, the researcher used cotton swabs to wipe the inside of the dryer and transferred the sample onto growth medium. The swab became visibly dark, indicating that a cocktail of germs had accumulated within the machine itself.

Inside many dryers, there may be:

• Dust from the room air
• Deposits from splashed water and aerosols from the toilet
• Organic material such as skin flakes and tiny droplets from exhaled air

When the machine is switched on, parts of this mixture can be broken into extremely fine droplets and blown around the room at high speed - precisely where people hold their faces and hands.

Do HEPA filters and UV light really help?

Manufacturers have responded to criticism in recent years by promoting “hygienic” models intended to clean the air stream. Two technologies are central to this approach.

HEPA filters - as used in aircraft and vacuum cleaners

HEPA filters, short for High Efficiency Particulate Air filters, are designed to trap a large proportion of tiny airborne particles, often down to 0.3 micrometres. Ideally, bacteria and many fungal spores are caught in the filter instead of ending up on users’ hands.

The theory sounds promising, but practical questions remain:

• How often do cleaning staff actually replace the filter?
• Is the filter disposed of correctly so that germs are not redistributed during replacement?
• Are all air paths within the appliance genuinely filtered, or are there routes that bypass the filter?

In some studies, HEPA-equipped machines perform considerably better than conventional models. Even so, the airflow is not completely germ-free.

UV light - germ-killing technology with many caveats

Some newer dryers use ultraviolet light internally to damage germs on surfaces or in the air. UV radiation can destroy DNA and thereby kill micro-organisms.

Its effectiveness, however, depends on several details:

• The strength of the radiation
• The duration of exposure
• The exact position of the UV module inside the appliance

If the exposure time is too short or the airflow is too fast, many germs survive their passage through the unit. In everyday use, that means UV dryers may reduce the risk, but they do not remove it altogether.

What does this mean for everyday toilet use?

The researcher’s experiment triggered a wave of online comments, from clinical staff to parents of young children. Many said they would avoid hand dryers in hospitals or schools in future.

Of course, avoiding washrooms altogether is not an option. However, there are practical ways to reduce personal risk:

• Choose paper where possible - Traditional paper towels mechanically remove some germs from the skin because they pick them up during drying.
• Avoid contact surfaces - After washing your hands, try not to touch door handles and buttons directly with freshly cleaned fingers; use a paper towel, for example.
• Wash hands properly and thoroughly - Use soap for at least 20 seconds, including between the fingers and around the nails. Anyone washing carelessly begins with more germs before using the dryer.
• Use hand dryers only briefly - If the air stream cannot be avoided, limiting use may at least reduce the “dose”.
• Keep your face out of the airflow - Hold hands as low as possible and keep your head as far from the outlet as possible.

When hand dryers become especially problematic

In settings such as hospitals, care homes and doctors’ surgeries, air dryers may create an additional risk. These places are more likely to contain people with weakened immune systems, while more resistant germs also circulate there.

At several hospitals in the UK and the US, hygiene teams now deliberately avoid hand dryers on certain wards and consistently use paper towels instead. Their concern is that air dryers could carry germs from toilet areas into corridors and patient rooms.

How germs spread so easily in the first place

One central mechanism begins before anyone even presses the dryer’s start button: the “toilet plume” phenomenon. Flushing produces fine droplets that rise invisibly into the air. They can contain bacteria and viruses and spread several metres.

When the lid is left open - or where there is no lid at all - these droplets settle on floors, washbasins, door handles and also on or inside hand dryers. There they remain until the next user activates the machine and stirs them up again.

People who better understand the risks often pay more attention automatically to apparently minor details: closing the lid before flushing, not touching the face directly with the hands, and not placing a phone on surfaces in the toilet.

What would need to change in the long term

For local authorities, shopping-centre operators and restaurant chains, the long-term question is clear: is eliminating paper towels really worthwhile if hand dryers increase the germ load in the room?

Possible measures for better everyday hygiene include:

• More washrooms fitted with well-maintained HEPA-equipped machines and clear maintenance schedules
• Combining paper towels and dryers rather than treating it as an “either-or” choice
• Better toilet ventilation systems to remove aerosols more quickly
• Clear guidance on correct hand hygiene directly beside the washbasin

Regardless of the technology, one point remains: clean, thorough handwashing greatly reduces the number of germs on the skin. What happens afterwards depends heavily on the drying method. Hand dryers may seem convenient and modern, but behind the warm airflow lies a hygiene issue that many people have underestimated.