I have a spray bottle of Iodophor, and a spray bottle of StarSan. Is there any issue with the two products reacting with each other? In other words, can I spray something with StarSan, and if I accidentally spray it again with Iodophor, is there any concern?
A good question might be "why"? Why spray a thing with two different but essentially identically functioning products? Use one or the other - there would seem to be little point in keeping and using both.
Iodine and phosphoric acid don't react in any lasting and poisonous way in the amounts that might be encountered in this situation. Its a moot point but one might even say that both work better together than either alone. However the iodine in the iodophor does form a complex with StarSans other ingredient - dodecylbenzenesulfonic acid and the toxicity of the complex is open to debate. IMHO in the very small amounts used to spray brewing equipment the risk is very low and I would suppose not much greater than the risk presented by any alkylbenzenesulphonic acid itself (as found in StarSan). So I personally would not be worried by this situation.
While it is not always practical, IMHO the best "no rinse" steriliser is boiling water. Even pasteurising at lower temps cures a multitude of "brewing sins" in an eco-friendly manner and with much less risk.