Usnea

What it is

Usnea is a slow-growing lichen — a symbiotic organism composed of a fungus and an alga — found hanging from trees in cool, moist environments. It is often called “Old Man’s Beard.” The part used medicinally is typically the grey-green, hairlike strands with an elastic white core. It has a long history in botanical medicine in Europe, Asia, and North America, chiefly for infections and wound care.

How it works

Usnea’s key bioactive constituents include usnic acid and polysaccharides. Usnic acid shows broad activity in vitro against Gram-positive bacteria, some fungi, and certain protozoa, by disrupting microbial energy production and cell membrane function. The polysaccharides appear to support innate immune modulation and may have mild antioxidant and anti-inflammatory effects. In topical form, the antimicrobial action predominates; in internal use, a combination of antimicrobial and immunomodulatory actions is sought.

Why it’s important

Usnea is valued in botanical medicine because it can act where antiseptic, non-systemic antimicrobial support is desired — for example, applied to contaminated wounds, burns, or abrasions to discourage microbial overgrowth, or used internally by practitioners to support the body’s response to upper-respiratory infections when bacterial overgrowth is suspected. It is also important historically as a pre-antibiotic era antimicrobial widely used in rural and field contexts where pharmaceuticals were unavailable.

Considerations

Usnic acid can be hepatotoxic in high doses or in susceptible individuals; serious liver injury has been reported, especially with concentrated internal products (notably some “fat-burner” formulas that contained high isolated usnic acid). Therefore, internal use requires professional oversight, conservative dosing, and avoidance in pregnancy, lactation, children, and people with existing liver disease or people taking hepatically metabolized or hepatotoxic drugs. People with autoimmune conditions or the immunosuppressed should not self-prescribe; immune-modulating herbs can be bidirectional and clinically contingent. From an ecological standpoint, Usnea grows very slowly and is sensitive to air quality and over-harvesting; use should favor cultivated or ethically harvested sources. Finally, in all cases of suspected serious or progressive infection, Usnea is not a substitute for timely medical evaluation or evidence-based antimicrobial therapy.