SUMMARY The terpene p,α‐dimethylstyrene was isolated and identified in the essential oil of distilled Mexican lime (Citrus aurantifolia, Swingle) but could not be demonstrated in oil expressed from Citrus aurantifolia. Experimental evidence is presented supporting a nonbiogenetic mechanism of formation of p,α‐dimethylstyrene in distilled lime oil from the acid‐catalyzed cyclization of citral. The mechanism involves novel reactions of citral and its reaction products that are not consistent with the classically accepted acid‐catalyzed reactions of citral and seem to provide an explanation for the appearance of p,α‐dimethylstyrene in other citral‐containing essential oils of the Rutaceae citrus plants.