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If the immune system of a healthy human just shut down completely and instantly (magic, nanotechnology, whatever), and after a certain time period it went back to normal, how much time without the immune system would be survivable?

There are real world examples of people with severely damaged immune system, but I don't know how total it was.

So, basically:

1. What length of time would be immediately or almost immediately fatal? (so even restoring it completely would not save from a quick death)




2. What length of time would be survivable but lead to long term (or permanent) consequences?




3. What length of time would be completely healable afterwards, even without modern medical treatment?




4. What length of time would be unnoticed or almost unnoticed?

Assume the victim of this curse is not doing anything dangerous or unsanitary during its effects. (so no cuts, bruises, being in an unsanitary environment, etc.)

Of course, as we have no real world data to measure it (AIDS-patients don't go from 100% to 0% in an instant), a rough Fermi estimation would be enough, but even for that I have no idea where and how to start.

In about 24-48 hours you'd start having skin condition from unchecked staphylococci and the like: eczema and erythrodermatitis. As soon as the skin barrier is broken, cellulitis and circulation problems will ensue, followed (since there's nothing to check the infection) by gangrene. I'd expect death from septic shock to occur inside of one week. Disabling will be severe within three days and pretty much complete inside of four or five.

So:

• 0 - 24 hours: no real effects except itching and rashes


• 24 - 48 hours: weeping sores, discoloration and loss of sensation in limbs and other areas. Some loss of functionality might be noticeable after healing.


• 48 - 72 hours: severe pain and gangrene. Even after immune system recovery, strong chances of amputation. Scarring, Permanent loss of some functionality.


• 72 - 96 hours: almost certain amputation, possible death by septic shock even after healing.

So, while in that time several nasty kinds of cancer are guaranteed to have sprung up, they won't be what kills you.

(If several brief immune loss periods repeat, however, it's possible for some of those cancers to develop enough to become dangerous).

Meanwhile, however, dormant infections might spring up and manifest (herpes, for example, and some fungal conditions). These will take longer to disappear even after healing (actually might surface some time after the immune system has recovered).

If you have a preexisting condition or eat anything that requires immune support (the bacteriocidal properties of saliva will still be there, but several kinds of sporae will not be killed and usually die when they germinate and get recognized by the immune system - so, now, that barrier no longer holds), then anything from cholera to Montezuma's Revenge can off you within 48 hours.

If you don't have complete immune deficiency, then you can survive indefinitely as long as you take sufficient precautions (this is the so-called "Bubble Condition" or "Bubble Boy Disease").

Something more than that, and you have something not too different from Acquired Immunodeficiency Syndrome - AIDS.

Since your body contains at least as many microorganisms of various kinds as it does human cells, which are continually kept in check by the immune system, I’d say that “a few hours” was a reasonable guess for your survival time with no immune system at all. You wouldn’t have to wait to be invaded by bacteria or viruses, the ones that would kill you are already there.