Enzymes are high-molecular-weight proteins and highly sensitizing occupational allergens used widely in industrial processes. Lactase has been described to cause work-related respiratory and conjunctival immunoglobulin (Ig)-E-mediated sensitizations in workers in the pharmaceutical industry. In these previous reports, allergic rhinoconjunctivitis or asthma was confirmed with prick tests but not by challenge tests. Lactase previously has not been described as a cause of immediate or delayed contact skin reaction. Furthermore, there are no previous reports of lactase-specific IgE. We report a case of protein contact dermatitis and allergic rhinoconjunctivitis from occupational exposure to lactase in a pharmaceutical worker. The patient exhibited strong positive responses to lactase in prick tests. In an open application test, lactase elicited whealing, and in patch testing, lactase elicited an eczematous reaction. Serum lactase-specific IgE antibodies were demonstrated in immunospot and radioallergosorbent test assays, and lactase-IgE-binding fractions and their specificities were examined in immunoblot and immunoblot inhibition assays. The chamber challenge test was performed to detect the association between lactase sensitization and rhinoconjunctival symptoms. Our results have confirmed the previous observations that lactase can induce occupational IgE-mediated respiratory and conjunctival sensitizations, but they show that contact skin reactions caused by lactase may also occur.