Previously, penicillins (PCN) and cephalosporins were produced with the same fungi during synthesis. This increased the rate of cross contamination especially prior to 1980. Although the allergy was though to be due to the similarities in the beta-lactam ring it is more probably caused due to manufacturing contamination although there is cross reactivity risk based on side chain similarity. 1st and 2nd generation penicillins share the same R-1 side chain. However, a current review of the literature demonstrates that the 10% or greater allergy may be exaggerated.