Seriously, it’s better to throw your underwear and socks into the washing machine than to wash them by hand!

When you are busy at work, you will inevitably want to be lazy when it comes to housework. Although you can't save your underwear and socks for a week before washing them, the thought of washing them by hand and rubbing them is tiring. So: can you wash your underwear and socks directly in the washing machine?

We conducted a survey and found that from the feedback of readers, quite a few people are used to washing underwear by hand. People generally feel that it is still unsafe to throw underwear into the washing machine. After all, we have also popularized science before that washing machines are not as clean as they look to the naked eye.

In fact, there are many studies on the sterilization effect of machine washing, which can provide enough confidence for machine washing users. Our cooperative expert "Tipsy Engineering Dog" also did a small family experiment, and the results once again made us sigh: This time, the lazy people won!

If you feel dizzy after reading the experimental process, you can go directly to the end of the article to read the summary, but the tipsy student said that he would be sad if you do so~

Hand washing is time-consuming and laborious , but may contain more bacteria than machine washing

The tipsy student prepared two pairs of socks that were washed and changed regularly (not too dirty), recorded the colony data of the socks in their initial state, then added ordinary laundry detergent and water, washed one by hand and the other by machine, and finally recorded the colony data after washing.

Image source: @Tipsy Engineering Dog

Place the socks in water approximately 20 times their weight and stir thoroughly. Take samples from the stirred water to test the total number of colonies. The sample numbers are marked as 1 (no dilution) and 2 (200-fold dilution).

As for why you see a fork, it is to prevent the bacteria on your hands from affecting the experimental data as much as possible, but the tipsy classmate did not have tweezers long enough at home, so he had to use a fork instead.

Image source: @Tipsy Engineering Dog

Take out a sock, pour enough laundry detergent on it, and rub it repeatedly for 3 to 5 minutes.

After rubbing, rinse repeatedly under the faucet until there is no greasy feeling of detergent. About 10 liters of water are used.

Image source: @Tipsy Engineering Dog

Place the wrung-out hand-washed socks in water about 20 times their weight and stir thoroughly. Take 1 ml of the stock solution sample from the stirred water to test the total number of colonies. The sample is marked as 3.

Image source: @Tipsy Engineering Dog

Take another sock, put it into the washing machine, add appropriate amount of detergent, and wash it with a batch of daily clothes. Select the default program of the washing machine and the washing temperature is 30°C. The total washing time is about 1 hour.

Don't worry, this fork will never appear in the kitchen again. (Although it's okay if it's sterilized at high temperature)

Image source: @Tipsy Engineering Dog

After washing, take out the machine-washed socks and place them in water about 20 times their weight and stir them thoroughly. Take 1 ml of the original solution sample from the stirred water to test the total number of colonies, and mark the sample as 4.

Image source: @Tipsy Engineering Dog

To ensure that any bacterial residue on the socks could be detected, we patiently waited for 24 hours.

The experimental results show that samples 1 and 2 have about 259 and 400 bacteria, respectively, indicating that the socks that are washed and dried at high temperatures normally have only a few hundred bacteria per milliliter, which is not a lot. (Many people may not have much idea about the total colony count, so it is better not to know the number. For reference, the national requirement for the total colony count of drinking water is less than 100 per milliliter to be qualified.)

In the hand-washed sample No. 3, 108 bacteria were still detected, indicating that hand washing cannot effectively remove bacteria from socks.

No bacteria was detected in the machine wash sample No. 4...

The tipsy student said that he had tried very hard to wash sample No. 3 by hand. Based on changing 2 socks and 1 pair of shorts every day, this level of hand washing would take about 15 minutes to rub and 10 minutes to rinse. There are only 24 hours in a day, and the awake time is 16 hours. Washing underwear and socks can take nearly 1/32 of one's life, but the result of this hand washing is not satisfactory.

Some students may also feel that this is just a personal experiment and cannot explain the problem.

We also found some experiments with larger sample sizes. Foreign studies have shown that a 45-minute washing program + a temperature of around 30°C + ordinary laundry detergent can remove bacteria at a rate of at least 99% and at most 99.9999%. Therefore, in the above experiment, it is normal that no bacteria can be detected after machine washing, with only a few hundred samples.

Add disinfectant and you don’t have to worry about machine washing

If you are still worried, you can add disinfectant when washing in the machine.

Image source: @Tipsy Engineering Dog

There is still a pair of socks left in the above experiment. Put it into the washing machine and mix it with other clothes. Follow the same procedure as the previous experiment, but add two bottle caps of disinfectant. After washing, take out the socks, soak them in water and take samples, marked as sample 5.

As a result, no bacteria were detected in sample 5 either.

Common clothing disinfectants, such as parachlorometaxylenol, need to be diluted in proportion before soaking the clothes for a while, rinsing them, and then washing them with detergent. If you do not soak the clothes in advance when washing by hand, the contact time between the disinfectant and the clothes will not be enough; and the temperature of hand washing drops quickly, so it is difficult for the disinfectant to be maintained above 30°C, and the activity is insufficient.

You don’t have to worry about this when using a machine wash. Most machines will heat the water temperature, and soaking takes time, but machine washing does not take up your time and has a better sterilization effect. Why not do it?

Washing with a high temperature in the washing machine or using a dryer will have a better sterilization effect

Studies have shown that high temperatures can significantly enhance the sterilization effect.

The tipsy student conducted another experiment using socks that had been worn for three days. After wearing them for three consecutive days, the number of colonies on the socks exceeded 100,000, which is comparable to "raising insects". After machine washing and high-temperature drying, only 21 colonies were detected.

In fact, washing underwear with other clothes together will indeed make it easier for them to pick up dirt and microorganisms from outerwear. This is why people "instinctively" think that underwear and socks are dirtier when washed together with outerwear and pants.

But the point is that hand washing does avoid this minefield, but apart from the time and effort it takes, its cleaning and sterilization effects are not very reassuring. If the hands or basin are contaminated with infectious pathogens, the weak sterilization ability of hand washing is more likely to bring them into underwear and socks. If the underwear and socks are contaminated, hand washing can easily transmit the germs to the hands, and then pass them to the hand towels through the hands, and then pass them to the hands of other family members through the hand towels...

Of course, the elders at home may think: Isn’t it just high temperature sterilization? Can’t it be cured by exposing it to the sun? However, the fabric materials and colors of underwear and socks are not suitable for long-term high temperature exposure, and they are easy to become hard and yellow. The program design of machine washing itself can fully achieve a dual-pronged effect of high temperature + disinfectant, both of which have sufficient sterilization effect.

In this comparison, it would be better to let parents spend less effort!

Worried about the washing machine being too dirty ? Just pay attention to these points

Washing machines that have not been cleaned or sterilized for a long time may indeed have excessive microorganisms in the drum. So what are microorganisms afraid of? High temperature, high-speed water flow, strong oxidants, and drying, we will give it a full set:
The cheap rags and hand towels at home should be washed every two weeks at most. Use washing machine detergent or disinfectant effervescent tablets and rags to wash at 90°C. Remember to select the rinse program more than 2 times to avoid detergent residue. In this way, not only can the rags be washed white and clean, but the inside of the machine can also be disinfected and sterilized.

Image source: @Tipsy Engineering Dog

Remember to completely empty the detergent dispenser tank from time to time and clean it; do not close the door of the washing machine after using it, keep it slightly open, and try to keep the inside dry.

If you happen to have a washer-dryer at home, you can run a wash + dry program to dry the rag, inner barrel, and outer barrel. It also comes with a high-temperature disinfection, so it's hard not to be clean.

Research Summary

The class representative will help you highlight the key points
Finally, let’s summarize, how can we clean underwear conveniently and hygienically?

1) First, follow the above methods to do a good job of sanitation maintenance of the washing machine;

2) If you have a dryer, just choose high temperature when drying;

3) If you have a washer-dryer, it doesn’t matter whether you wash the clothes separately or mixed, just use a set of washing and drying programs to dry them completely;

4) If you don’t have a washer and dryer or a dryer, you can wash your underwear separately in the machine with the water temperature set to 60°C, or use disinfectant and mix it with other clothes.

5) If a family member already has a transmissible skin disease, they should be actively treated first. During the infectious period, the patient's clothes and utensils should be washed separately using the method described in point 4, or follow the doctor's advice.

Laziness drives the progress of human society. Have you learned today’s skills?

References

[1] Bloomfield, SF, Exner, M., Signorelli, C., Scott, EA (2013) Effectiveness of laundering processes used in domestic (home) settings. International Scientific Forum on Home Hygiene

[2] Hammer TR , Mucha H , Hoefer D . Infection risk by dermatophytes during storage and after domestic laundry and their temperature-dependent inactivation.[J]. Mycopathologia, 2011, 171(1):43-49.

[3] Honisch M, Stamminger R, DP Bockmühl. Impact of wash cycle time, temperature and detergent formulation on the hygiene effectiveness of domestic laundering[J]. Journal of Applied Microbiology, 2015, 117(6).

[4] Tano E , Melhus A . Level of decontamination after washing textiles at 60°C or 70°C followed by tumble drying[J]. Infection Ecology & Epidemiology, 2014, 4(1):24314-.

[5] Brusdal R. An investigation of domestic laundry in Europe - habits, hygiene and functional performance. 2003.

[6] Bockmühl, D. (2017), Laundry hygiene—how to get more than clean. J Appl Microbiol, 122: 1124-1133. https://doi.org/10.1111/jam.13402

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Source: DingXiang Life Research Institute This article is authorized to be reproduced from DingXiang Life Research Institute (ID: DingXiangLab) and may not be reproduced without authorization

Cooperating expert丨Tipsy engineer Master of Chemical Engineering from École Polytechnique Nationale Supérieure de Lorraine, France Home appliance science blogger

Scientific review | Sun Yafei, PhD in Chemistry, Tsinghua University

Editor | Wang Mengru