In order to understand how long coronaviruses can last on surfaces, and also which disinfectants will destroy them, we have to understand more about the overall construction of viruses in general, and coronaviruses in particular. For something so fundamentally simple as a packet containing ‘copy me’ information and a few key proteins, viruses come in a dizzying array of variations. Some viruses contain one long stretch of genetic material; others carry their information in fragmented pieces. Some contain information as double stranded DNA, like our own cells do, but others use single stranded DNA, double stranded RNA or even single stranded RNA. Flu viruses, for example, are RNA viruses that keep their genetic material in multiple fragments. Coronaviruses are also RNA viruses, but they carry their genetic material in a single long piece of RNA.
How the genetic material of a virus is ‘wrapped up’ also varies widely from virus group to virus group. Some viruses simply wrap their genetic material in proteins that protect it, and which also bind targets on the surfaces of cells they can infect. Others are more complicated in their overall packaging. Viruses in the Coronavirus group have a single long strand of RNA wrapped in a protein shell, or ‘capsid’. Surrounding that protein shell is an envelope of material snatched from the cell membrane of the host cell the virus was manufactured in. I guess you could say they have ‘stealth technology’, because their outermost surface looks like the surfaces of the cells it infects, with some key exceptions. In order to get in or out of a host cell, the virus must make its own virus-specific proteins. Coronaviruses force their host cells to make virus “spike proteins” that are stuck in this outer envelope in a way that makes the virus look like it has a halo or crown around it in electron microscope images, which is where the name “corona” comes from.
This envelope around the coronavirus makes it very tricky for our own bodies to recognize it as foreign and bad, which is why our innate immune systems don’t always block it before it establishes an infection. However, this same feature also makes the virus much more sensitive (read: easy to destroy) than non-enveloped viruses. The envelope that surrounds the coronavirus, like the membrane around our own cells, is a fragile structure made up of a particular type of oil molecule. Its whole structure is held together simply by the presence of water inside and outside the virus (or cell), forcing this oil molecules into a well-organized thin layer, the envelope (or ‘cell membrane’).
So what destroys an enveloped virus? Anything that makes the envelope, the proteins, or the genetic material (RNA) nonfunctional.
How long can it last in the environment?
The envelope is sensitive to desiccation, because if it fully dries out, it loses its structure and falls apart. Because the virus needs the spike proteins that are embedded in the envelope to infect a cell, the loss of the envelope makes the virus nonfunctional. But desiccation occurs at different rates on different types of surfaces, and will occur slower or faster depending on temperature, humidity, exposure to sun, etc., All viruses are also sensitive to UV light. Just as UV light causes damage to the DNA in our own skin cells, it also damages the genetic material, DNA or RNA, of viruses.
The coronavirus’s sensitivity to temperature, humidity and sunlight means that coronavirus can last for different lengths of time on different types of surfaces and under different conditions. We don’t really know exactly how long it can last under these different conditions without testing it experimentally. A group of researchers did just that (see this link for their science article: https://www.nejm.org/doi/10.1056/NEJMc2004973, or this news article about the same publication: https://www.businessinsider.com/coronavirus-lifespan-on-surfaces-graphic-2020-3). They found that the virus can remain active in ‘aerosols’ (droplets in the air from sneezes or coughs) for three hours or possibly longer. It only lasts about four hours on copper, less than a day on cardboard (or paper), around two days on stainless steel, and two to three days on plastic. These tests were done at 70 degrees Fahrenheit, 40% humidity, with no UV exposure. Scientists expect that these survival times will decrease with increasing temperature and/or exposure to sunlight.
I would like to point out that people who choose to wear gloves to protect themselves from coronavirus are generally choosing latex or some form of plastic glove… Based on the data in the study above, I would strongly recommend washing gloved hands, or even changing gloves, often, because I bet those virus particles survive for a long time on the surface of those gloves. Perhaps cloth gloves would be more appropriate… with their porous and absorbent surfaces, similar to cardboard, maybe the virus wouldn’t survive as well on the cloth, and they could simply be thrown in the laundry or washed in the sink rather than being thrown in the trash. I have no evidence to support that statement, its just a guess, but the data does hint strongly that the virus can last a long time on surfaces similar to plastic…
How can you clean it off surfaces?
The coronavirus envelope is sensitive to any chemical that disrupts oils… like soaps. Picture what happens to the oil layer on a dirty pan or dish in your kitchen sink when you add dish soap. The oil looks like it disappears. It didn’t actually disappear – the soap disperses it into millions of tiny little mini oil droplets. Now picture what happens to a coronavirus envelope when you put hand soap on it… The soap turns the envelope until a bunch of tiny oil droplets, and without a complete envelope, the virus can no longer attach to and infect host cells. By washing your hands vigorously for twenty seconds, you are physically removing viral particles by rubbing and running your hands under water, and you are making sure that soap gets into all the small cracks and fingerprint wrinkles present in your skin, where coronavirus particles might be hiding.
Alcohol is similar to soaps in how it affects oils. Weirdly, oil can dissolve in alcohol (specifically ethyl alcohol), and alcohol can dissolve in water, but oil can’t dissolve in water… Regardless, because oils can dissolve in alcohol, alcohol-based disinfectants can disrupt the envelope of a coronavirus by dissolving it. The key factor is that the alcohol concentration has to be high enough that it can dissolve the envelope. The CDC recommends that alcohol-based sanitizers must contain at least 60% alcohol (or the equivalent of 120 proof) in order to work, preferable 70% alcohol. In other words, any alcohol-based hand sanitizer you are using must smell basically like grain alcohol or 151 rum. Alcohol evaporates, so any bottle that has been opened will slowly be losing alcohol over time. If you can’t smell the alcohol, strongly, it doesn’t have enough to work against coronavirus.
A number of other chemicals disrupt the coronavirus structure, including quaternary ammonia, hydrogen peroxide, and the big gun, bleach. Quaternary ammonium compounds are common industrial/healthcare disinfectants, and are more potent than straight ‘ammonia’ when it comes to disinfection. Examples of quaternary ammonia compounds are cetrimide, benzalkonium chloride, cetylpyridinium chloride, and a number of others with even longer names. These cleaners interfere with both the viral envelope and viral proteins. Hydrogen peroxide and bleach are similar in how they work. Both are ‘oxidizers’ – they interact directly with organic molecules (oils, proteins, genetic material), changing and even breaking the bonds between the individual atoms in those molecules. Household bleach, or sodium hypochlorite, is a very strong oxidizer. No organism on the planet is immune to the effects of bleach. When any organic molecule is exposed to bleach, it experiences irreparable damage. Viral envelopes, spike proteins, capsid proteins, RNA… all fall before the power of bleach.
Quaternary ammonia, hydrogen peroxide and bleach also damage the organic molecules in our own cells, and must be used with care. They can only be used if diluted, and we must limit exposure to our skin (I hope I don’t have to say that we definitely can’t get them in our eyes, nose, mouth… and we REALLY can’t drink them!). The outer layer of our skin is made up of dead cells that are shed and replaced daily. While our skin can withstand some exposure to these strong chemicals, repeated exposure, or exposure to concentrated forms, can cause damage not only to the outer dead layers of our skin but also the deeper layers which have living cells.
For specific recommendations about how to disinfect surfaces, you should follow the CDC guidelines, which can be found here: https://www.cdc.gov/coronavirus/2019-ncov/prepare/cleaning-disinfection.html. I know that washing hands and not touching your face between washes may seem like an overly simple suggestion, but I hope that I have made a strong case that it is actually a very effective way to get rid of this virus from hands and any surfaces.
Science in Translation 