Scientists in Germany pitted chamomile oil, anise oil, dwarf-pine oil, manuka oil, and lemon oil against HSV-1 in test tubes. Manuka comes from the same plant family as tea tree.
All of the oils showed "high levels" of antiviral activity, even against HSV-1 strains that don't respond to the antiviral drug acyclovir, the researchers report.
They included Paul Schnitzler, PhD, of the Hygiene Institute at Germany's University of Heidelberg.
Of all the oils that were tested, chamomile oil was particularly good at targeting HSV-1, and it probably wouldn't cause irritation if applied to the skin, note Schnitzler and colleagues.
They didn't actually try applying chamomile oil (or any of the other oils) to cold sores.
But chamomile oil and other essential oils "might be suitable" for topical application in recurrent HSV-1 infection, even when those infections are resistant to acyclovir, the scientists write.
Their results were presented on Sept. 30 in San Francisco, at the American Society for Microbiology's 46th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy.