Southern Elder (Sambucus nigra or closely related species) has a long history of traditional use in herbal medicine, particularly in Europe and North America. Traditionally, elder flowers and berries have been used to support the immune system and to treat various viral infections, including colds and influenza. The use of Southern Elder for cold sores (herpes labialis) is primarily based on this broader antiviral folklore rather than direct, specific evidence for herpes simplex virus (HSV-1), the cause of cold sores. There are historical references to elderberry preparations being applied topically or taken internally for skin eruptions and sores, which might include cold sores by association.

Scientifically, laboratory research has shown that elderberry extracts possess general antiviral activity against certain viruses, but there is little to no robust evidence demonstrating direct efficacy against HSV-1 in humans. Most clinical studies with elderberry focus on influenza or common cold symptoms rather than cold sores specifically. Therefore, while the traditional use of Southern Elder for viral conditions is established, the specific application to cold sores is not supported by strong scientific validation, and the overall evidence for its effectiveness in this context remains weak.