It's been said that SARS-CoV-2 can remain on surfaces up to 9 or 10 days. While I read that smallpox can survive out of a host even for years.

As much as I know, since viruses are only protein capsules around RNA strands, thus they are comparable to rocks or metals. Why do they die out of a host?

What happens to them that causes them to die? Do they consume energy and run out of fuel? Do they have mysterious half-life as in chemical elements? Do they have predators in food- chain and get eaten by something else?

Why a surface diagnosed with a virus today, is clean after X daya/months/years? What happens to viruses on that surface?

I searched this and I couldn't find answera for why. They only say how long it survives.

  • 4
    They're not alive in the first place – Graham Chiu Apr 1 '20 at 10:33
  • So, what happens to these non-alive things after some time? Why surface becomes clear? – Saeed Neamati Apr 1 '20 at 11:19

TL;DR: Factors such as UV light and heat causes the mix of RNA, fatty membrane, and protein making up the viruses to steadily break down.

More details:


Strictly speaking, viruses can’t die, for the simple reason that they aren’t alive in the first place. Although they contain genetic instructions in the form of DNA (or the related molecule, RNA), viruses can’t thrive independently. Instead, they must invade a host organism and hijack its genetic instructions.


Just hanging about in the atmosphere, the effect of factors such as UV light and heat causes the mix of RNA, fatty membrane, and protein making up the [viruses] to steadily break down in a few hours [or less/more].

https://www.statnews.com/2020/03/19/coronavirus-survives-on-surfaces-how-to-protect-yourself/ (mirror):

Viruses covered in “envelopes” have the most trouble surviving outside a living cell. On surfaces, the surrounding light, heat, and dryness break down the envelope, killing the virus. (Porous surfaces pull moisture away from viruses that land on them, accelerating the destruction of the envelope.) Most rhinoviruses have such envelopes; so do some influenza viruses. Norovirus doesn’t, enabling it to last longer in the environment.

  • So, based on the links you sent, if we remove those environmental harsh conditions, a virus can exist and not be destroyed for unlimited time, unless its atoms and molecules somehow change. In other words, it's like a peice of rock that we can keep in museums for centuries, or even millenials. Is that true? – Saeed Neamati Apr 1 '20 at 17:09
  • 1
    @SaeedNeamati true, e.g. en.wikipedia.org/wiki/Pithovirus – Franck Dernoncourt Apr 1 '20 at 17:10
  • Comments are not for extended discussion; this conversation has been moved to chat. – Carey Gregory May 28 '20 at 23:35

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