Released April 20, 2026

About the Episode

In this installment, Dr. Auwaerter provides a practical overview of cellulitis, focusing on the evaluation of non-resolving cases, the role of non-infectious mimics, and the risks associated with commonly used over-the-counter topical antibiotics.

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Episode Summary

Dr. Auwaerter opens with a recent case involving a patient who developed redness around a minor laceration after striking a piece of furniture. Despite being started on cephalexin, the patient’s condition failed to improve, prompting a closer look at the underlying cause. Dr. Auwaerter uses this as an opportunity to remind clinicians that while streptococcal disease remains the most common cause of cellulitis, static changes within the first two to three days are not necessarily alarming. Cellulitis, particularly in the lower extremities, can take time to resolve due to toxin-mediated erythema.

Dr. Auwaerter then walks through the differential for non-resolving cellulitis. More serious causes like abscesses and necrotizing fasciitis are typically accompanied by systemic toxicity, while rare atypical pathogens such as non-tuberculous mycobacteria and Vibrio species should also be considered. Notably, up to one-third of presumed cellulitis cases may be non-infectious, with common mimics including stasis dermatitis, lymphedema, deep vein thrombosis, gout, pseudogout, and vasculitis. Elevating the affected limb above the heart is a practical way to help distinguish these from true infectious cellulitis.

The central teaching point centers on the patient’s use of bacitracin. Both bacitracin and Neosporin can cause allergic contact dermatitis with repeated use, particularly in previously sensitized individuals. Discontinuing it led to full resolution—the patient likely never needed systemic antibiotics at all. Dr. Auwaerter concludes by stressing that these topicals have no established role as adjunctive therapy in cellulitis, and that dermatologists often recommend plain petroleum jelly as a safer alternative. Clinicians should routinely ask patients about topical products they may be using, as allergic dermatitis from these agents is an easily overlooked cause of apparent antibiotic failure.

About the Presenter

Paul Auwaerter, MD, MBA

Paul G. Auwaerter is the Sherrilyn and Ken Fisher Professor of Medicine at the Johns Hopkins University School of Medicine serving as the Clinical Director for the Division of Infectious Diseases and Director of the Sherrilyn and Ken Fisher Center for Environmental Infectious Diseases.

He serves as the Executive Director of the Johns Hopkins Point of Care-Information Technology (POC-IT) Center producing the Johns Hopkins Guides – Antibiotic (ABX) (Antibiotic), HIV, Osler, Psychiatry, and Diabetes Guides. In 2018, Dr. Auwaerter served as President for the Infectious Diseases Society of America, the largest professional society worldwide related to infectious diseases.

For More Information

Johns Hopkins Antibiotic (ABX) Guide: https://www.hopkinsguides.com​

Unbound Medicine: https://www.unboundmedicine.com