If a person takes one puff how long will it stay in your system?

About 1 week. That is if you are clean to begin with. *** I guess it depends on what you were smoking. A normal cigerate will deposit nicotine in your blood which can remain in your system for up to 36 hours. On the other hand if it was a joint the THC deposited into your blood can last up to 90 days...but with such a low amount entering your system it is likely it will only last about 3 days unless you have been smoking it on a regular basis.