It can, in a minority of people. Double-blind additive challenges in people with chronic urticaria have reproduced hives and swelling with benzoate, and benzoates are one of the standard preservative groups tested in that work. The important caveat is that most people who suspect an additive turn out not to react on challenge, so the way to know is a proper trial: cut benzoate-preserved drinks and sauces for two to three weeks, then reintroduce one at a time and log what happens.

It can, in small amounts, when benzoate and ascorbic acid (vitamin C) sit together in an acidic drink, especially if it is stored warm or in the light. Testing in the mid-2000s found a handful of drinks above the drinking-water limit for benzene and most brands reformulated afterwards, either dropping the benzoate or the added vitamin C. It is not a reason to panic about a single bottle, but it is why the benzoate plus vitamin C pairing is worth noticing on a label.

No. The RPAH elimination diet removes the benzoate preservative numbers (210 to 213) along with sorbates, sulphites, nitrites, synthetic antioxidants, added colours and flavour enhancers. If you are doing a failsafe trial, benzoate-preserved cordials, juices and sauces come out for the elimination phase and go back in as a single named challenge.

Chemically it is the salt of the same acid. Benzoic acid occurs naturally in cloudberries, cranberries, lingonberries and in spices such as cinnamon and cloves, and in the stomach the added preservative becomes benzoic acid too. That matters practically: if you are benzoate sensitive, an additive-free label does not guarantee a benzoate-free food, and the naturally rich berries are worth logging as well.