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Usnic Acid

What is usnic acid? Why do we need it?

Usnic acid is a type of chemical extracted from usnea, a type of lichen also known as old man's beard, because of its resemblance to human facial hair. When extracted from the plant, it is yellow and crystalline in appearance. Mixed with water, however, it loses its yellow tint and appears colorless.

Usnic acid is known to exhibit antibacterial properties. In the United States, usnic acid (as a powder or ointment) is used to treat primarily skin infections, and has been shown to be effective in treating tuberculosis bacteria, as well as other pathogenic fungi. Pure usnic acid is also used in many types of creams, toothpastes, deodorants and sunscreens as a protectant and a preservative. Externally, it has been used to treat conditions such as ringworm and athlete's foot. It is used both in humans and on animals.

How much usnic acid should I take?

The amount of usnic acid to be taken depends on the condition being treated. The typical internal dose is between 30 and 60 drops of an usnic acid tincture, delivered three to four times a day. Larger doses can be used if usnic acid is being applied to the skin.

What are some good sources of usnic acid? What forms are available?

The leading source of usnic acid is usnea; it is usually extracted from the plant's cortex. Usnic acid is available as a pill, powder, extract and tincture.

What can happen if I don't get enough usnic acid? What can happen if I take too much? Are there any side-effects I should be aware of?

Because usnic acid is not considered an essential nutrient, minimum and maximum daily levels have not been established. However, long-term use of high levels of usnic acid may cause muscle fatigue and malaise. These conditions will resolve by discontinuing use. Some individuals may be sensitive to usnea and develop an irritation of the skin or throat. Again, these conditions will resolve if one discontinues use of usnic acid. There is also animal evidence that suggests usnic acid may have a toxic effect on the liver. As such, it should be used with extreme caution. As always, make sure to consult with a licensed health care provider before taking usnic acid or any other herbal remedy or dietary supplement.


  • Francolini I, Norris P, Piozzi A, et al. Usnic acid: a natural antimicrobial agent able to inhibit bacterial biofilm formation on polymer surfaces. Antimicrobial Agents and Chemotherapy November 2004;48(11):4360-4365.
  • Han D, et al. Usnic acid-induced necrosis of cultured mouse hepatocytes: inhibition of mitochondrial function and oxidative stress. Biochem Pharmacol 2004;67:439-51.
  • Hobbs C. Usnea: The Herbal Antibiotic. Santa Cruz, CA: Botanica Press, 1990.
  • Okuyama E, Umeyama K, Yamazaki M, et al. Usnic acid and diffractaic acid as analgesic and antipyretic components of usnea diffracta. Planta Med April 1995;61(2):113-5.
  • Rafanelli S, Bacchilega R, Stanganelli I, et al. Contact dermatitis from usnic acid in vaginal ovules. Contact Dermatitis 1995;33:271.
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