First, it may sound weird, but viruses are never alive. They have some of the characteristics of living things, like having DNA or RNA. They evolve. But they are not made of cells and they can't reproduce on their own. They multiply by invading their host's cells and turning them into virus factories. Some people refer to virus particles as "genes in a box." The box is a coat of protein.

But I understand the question you are actually asking, which is how long the virus particles can last outside our bodies before they fall apart. That's a complicated question. Each type of virus is different. The environmental conditions also make a big difference, but even then, the "best" temperature and humidity varies by the type of virus. So does the optimum surface (metal, cloth, etc.).

I'm going to take a wild guess that you might be interested in the COVID 19 virus. Experts are still figuring all of this out. The CDC says:

"Generally coronaviruses survive for shorter periods at higher temperatures and higher humidity than in cooler or dryer environments. However, we don’t have direct data for this virus, nor do we have direct data for a temperature-based cutoff for inactivation at this point. The necessary temperature would also be based on the materials of the surface, the environment, etc."

The information I have seen is between 4 hours and 5 days, depending on the material of the surface and environmental conditions. Your best bet is to avoid touching things outside your home. After contact with something from outside your home, wash your hands with soap and water, definitely before you touch your face, eat, or start touching other things around the house.

I found a technical article that summarizes persistence times for several other types of viruses:

"Most viruses from the respiratory tract, such as corona, coxsackie, influenza, SARS or rhino virus, can persist on surfaces for a few days. Viruses from the gastrointestinal tract, such as astrovirus, HAV, polio- or rota virus, persist for approximately 2 months. Blood-borne viruses, such as HBV or HIV, can persist for more than one week. Herpes viruses, such as CMV or HSV type 1 and 2, have been shown to persist from only a few hours up to 7 days. More information.

If you think it would be interested in a career in studying viruses and bacteria, you might look into becoming a microbiologist or epidemiology.

There is no singular answer to how long a virus can live outside our bodies.

We know that viruses can survive on surfaces and be infectious but its length varies greatly. For example, rhinovirus — the viruses that cause the common cold — will survive for less than an hour on surfaces. However, others such as the norovirus, which is a virus that can cause vomiting and diarrhea — can survive for weeks.

It is also not as simple to do lab experiments to figure out the infectiousness and longevity of a virus outside the host body. Therefore we need more robust data to confirm that for various different types of viruses. SARS-CoV-2 is a very recent virus and researchers are trying to figure out how long it will live on an inanimate surface.

This is a tricky question. Viruses aren't really "alive"- and studies that report how long viruses last on surfaces outside the body might not all be examining the same question. You can measure how long a virus remains "detectable" on a surface. This usually means that there are remnants of virus DNA on the surface, and it is common for these to be detectable for weeks. But just because the DNA is detectable does not mean the virus could still infect you. So the more important question is "how long does a virus remain infectious when it is outside our bodies?".

Unfortunately, it depends on a lot of factors: the type of virus, the type of surface, the temperature, the humidity, and many others. Norovirus (stomach bug) is particularly hardy, and may remain infectious on surfaces for several weeks. For influenza viruses, this timeline is more like a day. HIV does not survive well outside the body, and loses its infectiousness very quickly at room temperature. Most viruses last longer on smooth, hard surfaces than they do on soft porous surfaces, and are likely to be damaged by high temperatures and UV light.

Here is a nice article, focused mostly on influenza, that discusses some of these issues in more detail: flu viruses on public surfaces

This depends on the virus. Many viruses create resistant coatings around themselves that allow them to survive longer than raw DNA or RNA could. However, the nature of the coating determines how long they can live outside, as well as what kind of conditions destroy them. As an example, the coatings of coronaviruses are made out of lipids, which dissolve in soap, and this is why washing your hands with soap is so effective at destroying any virus particles on your hands.

Great question, the answer is it depends. Flu virus survives on a hard surface for up to 24 hours. A common cold may survive up to 7 days. Most viruses may survive but quickly lose the power to infect anybody. However washing your hands with soap and water is the best way to get rid of viruses!

This is really useful - it explains that the big question is : How Many viruses get inside us?

"3. Why a virus blog post went viral
By now, a friend may already have forwarded you a much-discussed blog post from a biologist named Erin Bromage — it has more than six million views. It’s an impressively clear explanation of how the virus often spreads inside confined spaces, like restaurants, churches, workplaces and schools.

Even when people remain more than six feet apart, they can become infected by breathing the same air as an infected person for an extended period of time, Bromage explains. Those scenarios, he argues, are more worrisome than a quick trip to the grocery store or almost any outdoor activity.

Background: Bromage told me that he began focusing on the virus in January to have a current example to use in his class on infectious diseases at the University of Massachusetts, Dartmouth."

For the corona virus, they think it can survive for up to 3 days on smooth surfaces but only 1 day on porous surfaces like paper.

Viruses are only partly alive, because they need to be in something alive before they can multiply. The link below uses 'survive' instead of 'live,' which I like.

How long can a virus live outside a body.