Experiments show that using a hand dryer after washing hands results in more bacteria than letting hands air dry naturally

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You wash your hands every day, but have you ever thought that the way you wash them might be completely wrong? Especially, use a hand dryer to blow on your hands after washing them. You don’t need to touch the dryer, which gives a feeling of cleanliness, but experiments show that using a dryer actually dirties your hands. Recently, a reporter visited a first-class food safety laboratory in Beijing and simulated normal hand-washing conditions by washing hands with hand soap in the restrooms of a fast-food restaurant and a KTV, followed by drying them with hand dryers. To compare the effects of the experiments, after washing their hands, the reporters had their right hand dried using a hand dryer while their left hand was allowed to air dry naturally. Then, the experimenters took samples from each hand to examine the level of bacteria on them under these different conditions. The experimental results showed that the colony counts of hands dried by heating increased by approximately 67% and 28%, respectively, compared to those dried naturally. A disease control expert in Beijing said that places where hand dryers are installed are usually quite humid, and bacteria tend to grow in these dryers; as a result, more bacteria are detected on the hands when using a dryer compared to when they are dried naturally. It is recommended to use the standard \"six-step handwashing method\" and let your hands air dry naturally. ■ Experimental samples: Hands were washed at a KFC fast-food restaurant and the restroom of a KTV on the East Third Ring Road. After drying the hands either using a hand dryer or by air-drying them, samples were taken from the hands for testing. Location of testing: A first-class food safety laboratory in Beijing; the number of bacteria increased by nearly 70% after use of the hand dryer. Sampling: Following normal washing habits, the reporter washed hands at the KFC fast-food restaurant near the laboratory and in the restroom of a KTV, using the same hand soap, and spaced out the two washing sessions. To compare the experimental results, after washing hands, the right hand was dried with a hand dryer while the left hand was allowed to air dry naturally. To prevent secondary contamination, it is necessary to return to the laboratory promptly, and the laboratory staff should use disposable quick-drying swabs to wipe samples from the reporter’s hands and place them in sterile nutrient solution. 2. Testing: Place the sample solution in a 9-ml test tube containing sterile saline. At the same time, another 10-fold diluted solution sample was prepared to create 1:10 and 1:100 sample suspensions. The solution samples of two different concentrations were placed in separate media, and the colonies were cultured at room temperature for more than 24 hours. Experimental results: After washing hands in the restroom at KFC and allowing them to dry naturally, the number of colony-forming units on the hands was 30 cfu/g (cfu/g is a unit used to measure the total number of microbial colonies per gram of sample); after drying the hands with a hand dryer, this figure rose to 50 cfu/g, an increase of about 67% ； After washing hands in the KTV restroom and allowing them to air-dry, the number of colony-forming units on the hands was 180 cfu/g; after drying the hands with a hand dryer, this figure rose to 230 cfu/g, an increase of about 28%. Experimental analysis: The experimental technicians explained that, based on the data from both groups, the number of bacteria on the hands after drying them with a dryer was significantly higher than when they were dried naturally, indicating that the dryer may have released some bacteria. Wrong hand-washing methods can result in 44 times more bacteria. 1. Sampling: The reporter first simulated areas in daily life where bacteria tend to accumulate, then washed the palms and backs of the hands briefly for less than 10 seconds before going to the laboratory to take samples. Subsequently, the reporter repeated the process of contacting areas where bacteria tend to thrive, using the correct hand-washing method recommended by the laboratory staff – the \"six-step handwashing technique\" – to clean the palms, backs of hands, knuckles, fingertips, spaces between fingers, and the undersides of fingers, for a duration of about 60 seconds, before promptly going to the laboratory to collect samples. 2. Detection: As with the method described above, the sample solution is placed in a 9-ml tube containing sterile saline, and then sample dilutions at 1:10 and 1:100 are prepared respectively. The solution samples of two different concentrations were placed in separate media, and the colonies were cultured at room temperature for more than 24 hours. Experimental results: After washing hands using the standard \"six-step handwashing method,\" the bacterial count on the hands was 120 cfu/g ； After washing hands with the ordinary method, the bacterial count on the hands reached as high as 5300 cfu/g. Experimental analysis: According to the experimental technicians, the bacterial count on the hands after ordinary handwashing is about 44 times higher than that after standard handwashing; it is recommended that everyone use the \"six-step handwashing method\". ■ Further investigation: The fryers in fast-food restaurants are only cleaned on the outside, not inside. Yesterday, reporters returned to the KFC fast-food restaurant and KTV where samples were taken for testing. The restrooms in KFC are located near the entrance, have good ventilation, and are constantly cleaned by maintenance staff. A cleaner said that those on shift have to wipe down the sinks and hand dryers several times, at least two or three times a day, but they do not clean the inside of the hand dryers, nor are they aware of whether bacteria might grow there. Compared to KFC, the restroom in the KTV where samples were taken was darker and had poor ventilation; moreover, the cleaning staff did not work on a shift basis, and they said that they did not clean the hand dryers frequently. The dryer manufacturers recommend cleaning the filter screens and carbon brushes weekly. Based on the product information indicated on the two dryers from which samples were taken, the reporter contacted the manufacturers of these dryers. A after-sales representative explained that this dryer produced by the company has a filter, and with frequent use, microorganisms may accumulate on this filter; it is therefore advisable to clean it once or twice a week. If it has been in use for more than two years or even longer, it is best to replace the filter directly. A staff member from another company said that it is not recommended to disassemble the interior of the dryer for cleaning, as it can lead to electric shock and damage to the machine. However, its dryer has a removable black carbon brush at the air outlet, which should be cleaned once or twice a week. ■ Experts say that the temperature of the warm air is not sufficient for killing bacteria. An expert from the Beijing Center for Disease Control and Prevention stated that the working principle of hand dryers relies on wind and temperature, and they emit warm air whose temperature is not high enough to kill bacteria. Moreover, bathrooms are usually damp, and in such a humid environment, bacteria tend to grow more easily inside hand dryers. Therefore, it is normal for there to be more bacteria on the hands after washing them and drying them with a hand dryer, compared to when they are dried naturally. Experts say that many people simply wash the palms and backs of their hands, without using hand soap or detergent, but washing hands for at least 20 seconds each time is necessary to be effective. At the same time, it is recommended that everyone use the “six-step handwashing method.” ■ The standard “six-step handwashing method”: 1. Place the palms together and rub them against each other with the fingers interlaced. 2. Rub the palms against the back of the hands along the spaces between the fingers, alternating sides. 3. Place the palms together again and cross the hands while rubbing them against each other along the spaces between the fingers. 4. Hold one hand with the other and rotate the thumbs while rubbing them together, alternating sides. 5. Bend the joints of each finger and rotate them while rubbing them against the palm of the other hand. 6. Rub the wrists, alternating sides. Rinse and dry under flowing water