Ultraviolet light kills the new coronavirus in 0.3 seconds? Is this reliable?

On the afternoon of November 29, the State Council's Joint Prevention and Control Mechanism held a press conference with the theme of "Implementing prevention and control measures in detail and effectively handling the epidemic." During the press conference, a reporter asked a question about ultraviolet and infrared disinfection.

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In response to this, experts from the Centers for Disease Control and Prevention gave a clear answer, which is that common ultraviolet light disinfection usually takes half an hour, and it may not be effective if the time is too short . Infrared disinfection is mainly used to disinfect heat-resistant tableware .

So is ultraviolet disinfection suitable for our daily home use?

Let me first say the conclusion. For home disinfection, ultraviolet light is not a good disinfection method . Even if we can follow the instructions for use for a sufficient period of time, it has many limitations and hidden dangers. It is not suitable for daily home use.

Let me explain in detail below.

01

Why can ultraviolet light disinfect?

The shorter the wavelength, the greater the energy of a single photon . When the energy reaches a certain level, it can destroy important molecules in organisms such as DNA and RNA, causing pathological changes or even death. For example, the wavelength of ultraviolet light is between 10-400 nanometers. The wavelength of ultraviolet light commonly used for disinfection is 253.7 nanometers, which belongs to the UVC band and has strong disinfection ability. After being irradiated by ultraviolet disinfection light for a period of time, the DNA in bacteria and viruses will be destroyed and cut off by the "high-energy" ultraviolet light, and then they will not be able to survive and reproduce normally, and will not pose a threat to humans.

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Ultraviolet disinfection does have many advantages. It does not require heating or soaking, and there is no residue after disinfection. All you need to do is ventilate the room to blow away the ozone.

02

Are UV lamps suitable for home use?

So the question is, with so many advantages, are UV lamps suitable for home use?

Ultraviolet disinfection has great limitations and is not recommended as a routine disinfection method at home. Let’s talk about the reasons below.

First, as we all know, light travels in a straight line, and ultraviolet light is also light. If it is blocked, its effect will be greatly reduced . This is why ultraviolet light is often used to disinfect smooth surfaces (no gaps and grooves that will not block light), air , and water (transparent). For example, the stainless steel clean bench in the laboratory is smooth inside, and ultraviolet light can be used to disinfect it for half an hour. In the operating room, ultraviolet light is often used to disinfect the air to prevent airborne bacteria from infecting patients. Sewage treatment plants use ultraviolet light to treat water.

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On the other hand, who doesn't have furniture, mats, sheets, carpets, etc. in our homes? These things either block light or have too many gaps, so ultraviolet rays can't get in, and naturally they can't achieve the disinfection effect. Some friends may ask, can I disinfect the air? Yes, but we can use air purifiers or open windows for ventilation to greatly reduce the amount of bacteria in the air in the house, and ultraviolet lamps are not necessarily required.

In addition, there is a hidden danger. As mentioned above, ultraviolet rays can destroy important molecules in organisms such as DNA and RNA, but they are not smart enough to distinguish "this is a bacteria to be killed" and "this is a person to be moved out of the way". If we forget to turn off the light when using it (fixed ultraviolet lamps often have this problem), or there are curious babies or elderly people who do not understand the harm of ultraviolet rays at home, and they move around within the range of ultraviolet light, they may burn their family members' eyes or skin, increasing the risk of eye diseases and skin cancer (see the news screenshot below). In addition, ultraviolet disinfection often produces ozone. If ventilation is not carried out in time, there will also be hidden dangers of ozone pollution, which may damage the respiratory tract of family members.

03

Is sterilization possible in 0.3 seconds?

Of course it is possible, but it will do more harm than good to the family . Why do I say that? There is a saying that goes, "Great power brings miracles." Take the laser pointers we usually use in class, for example. They are also lasers, but the power is very low, so they are mild and harmless. However, if the power is slightly increased, it can easily burn through balloons and paper cups.

The same is true for ultraviolet lamps. As long as the power is high enough, theoretically it can kill germs instantly. However, if used on a daily basis, such high-power ultraviolet lamps may become a "weapon."

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We can think about it, if it takes half an hour to use an ordinary sterilization ultraviolet lamp, the power may need to reach thousands or even tens of thousands of times to "kill" the bacteria in seconds. If such strong ultraviolet rays are not used carefully and shine on family members, it is likely to cause irreversible consequences.

This is why UV disinfection equipment is also divided into civilian and medical use (with different difficulty, power and efficiency), and they all have power regulations to ensure that even if people are accidentally exposed to UV light for a short period of time, they will not be seriously harmed. In this way, although disinfection may take a little longer, it is less likely to cause accidents.

Even if you really plan to use ultraviolet light disinfection at home, please read the instructions carefully , understand the key points such as irradiation time and effective distance, and make reminders. Avoid family members from entering the room where ultraviolet light disinfection is being used. In addition, ultraviolet lamps usually need to be cleaned and replaced regularly to avoid reduced disinfection effect due to stains or aging of the device.

Finally, to sum up, ultraviolet disinfection is probably not a good choice for our average family, and it is not necessary to buy it . Even if there is an epidemic around, daily household disinfection, wiping with medical alcohol, wiping with chlorine-containing disinfectants according to the concentration in the instructions, and opening windows for ventilation are sufficient.

Author: Ding Zong

Review | Tang Qin, Deputy Secretary-General and Researcher of the Science Popularization Expert Committee of the Chinese Medical Association

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