It depends on the bottle. The traditional British recipe uses barley malt vinegar, which contains gluten, so those versions are not coeliac safe. The American formulation of Lea and Perrins is made with distilled white vinegar and is labelled gluten free. Supermarket own brands go both ways. Because the sauce grades only moderate rather than high on gluten, the practical rule is to check the vinegar named in the ingredients each time you buy.

Typically yes, at a moderate level. Sulfites come with the vinegar and molasses base and are sometimes added as a preservative, and many bottles declare them. The dashes used in cooking are small, but if you already react to wine, dried apricots or pickled foods it is worth counting Worcestershire in your daily sulfite total rather than treating it as a free seasoning.

Yes. Anchovies are fermented into the base and are what gives the sauce its savoury depth, so it is not vegan and it is unsafe with a fish allergy. This catches people out constantly because the sauce is invisible once it is in a dish. Caesar dressing, bloody Marys, cottage and shepherd's pie, gravies and steak marinades are the usual hiding places, and a few anchovy-free versions are sold specifically for this reason.

It rates mild rather than high, which surprises people given that it is fermented, aged and built on vinegar and anchovy. The reason is quantity: a dash contributes far less than a portion of aged fish or cheese, and its tyramine and free glutamate ratings are mild for the same reason. If you are very histamine sensitive, the risk is in recipes that use it by the tablespoon, not in a shake over a hot dish.