Studies raise questions; harm in humans has not been established.
Sodium benzoate is permitted in the US, EU, UK and other major markets, and no authority has moved to ban it. FDA lists it as Generally Recognized As Safe (21 CFR 184.1733). EFSA's 2016 re-evaluation retained a group acceptable daily intake of 5 mg per kg of body weight, while noting some high-consuming groups may exceed it.
The documented concern is conditional rather than general, and worth stating precisely because it is often reported loosely. Benzoate salts can react with ascorbic acid (vitamin C) to form benzene — a known human carcinogen — at very low levels, and heat and light accelerate this. It is a formulation-and-storage issue, not a property of the preservative on its own: a pickle jar containing sodium benzoate and no vitamin C has no pathway to form benzene. FDA analysed beverages in 2005-2007 and found most contained no detectable benzene or levels below the 5 ppb drinking-water limit; a small number exceeded it and were reformulated or discontinued, with reformulated products then testing below 1.5 ppb.
Sodium benzoate also featured in the 2007 Southampton study on children's hyperactivity, but it was administered alongside artificial colours, so that study cannot separate any effect of the benzoate itself. The warning-label rule that followed in the EU applies to the six colours, not to sodium benzoate.