Patient reports of allergic reactions to local anesthetics are fairly common, but investigation shows that most of these are of psychogenic origin. Psychogenic reactions are often misdiagnosed as allergic reactions and may also mimic them, with signs such as urticaria, edema, and bronchospasm. True allergy to an amide is exceedingly rare, whereas the ester procaine is somewhat more allergenic. An allergy to one ester rules out use of another ester, because the allergenic component is the breakdown product para-aminobenzoic acid, and metabolism of all esters yields this compound. In contrast, an allergy to one amide does not rule out use of another amide. A patient may be allergic to other compounds in the local anesthetic, such as preservatives in multidose vials.