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By Vance Dietz, MD, MPH, TM
"Five things have been said about garlic: it assuages hunger, warms the body, brings joy, increases virility, and destroys intestinal lice. There are those who say it engenders love and dispels envy."
Babylonian Talmud: Baba Kama
Skin infections! whether fungal or bacterial in origin, they are some of the most common medical problems that a person has to deal with.
Garlic! Whether slivered or minced, or used as whole cloves or crushed, it is probably one of the most common aromatics used in cooking. Garlic not only gives flavor to food, but according to some is good for other uses as well. For example, when worn around the neck during a full moon, it has been reported to keep vampires at bay. Others suggest that garlic is better for treating infections than dealing with vampires.
Garlic in Medicine
Allium sativum, also known as poor man’s treacle or clove garlic, is said to have originated in Central Asia. Eventually introduced into the Mediterranean area, it is now cultivated worldwide.
The medicinal parts of garlic are the whole fresh clove, the dried clove, and the oil prepared from the clove. The ancient Egyptians, Greeks, Romans, Babylonians, and Chinese all knew of garlic’s healing ability.1 In Egypt, the Codex Ebers Papyrus (1550 B.C.) mentions the healing power of garlic. Pliny the Elder wrote about the medicinal uses of garlic. In 3000 B.C., Herodotus mentioned the medicinal use of garlic.2
Hippocrates is said to have used garlic in the fifth century B.C. to treat infections, including leprosy. In 1722, citizens of Marseilles were reported to be protected from the plague if they used an internal preparation of garlic vinegar. In 1858, Louis Pasteur reported favorably on the antibacterial activity of garlic. Currently, garlic is said to aid in the lowering of serum lipids and to prevent age-dependent vascular changes.3
Garlic was used in Europe for bronchitis, colds, and hay fever.1 In parts of Mexico, garlic is used to treat snake bites and, when taken internally, for the treatment of pertussis. In American folklore, garlic was put into old socks and worn around the neck to cure colds and to ward off evil spirits. When taken internally, it has also been used for atherosclerosis, high blood pressure, bloating, menstrual pains, and as a tonic. External uses include the treatment of corns, warts, calluses, otitis externa, muscle pain, neuralgia, arthritis, and sciatica.4
Mechanism of Action
The exact mechanism of action is unclear. Garlic contains alliins, ajoene, fructosans, and saponins.4 An alliin, diallyl thiosulfinate, is thought to be responsible for garlic’s antibacterial and antifungal properties.5 In China, another alliin, diallyl trisulfide, is used for the treatment of bacterial and fungal infections. Garlic intake in humans has been reported to enhance natural killer cell activity and immune activity.6,7
Sorrentino reports, "When raw garlic is cut or crushed, the enzyme allinase interacts with the cysteine compound alliin to produce allicin. Allicin gives garlic its typical aroma and taste.... Allicin is also thought to be one of the most important medicinal substances in garlic, although little or no allicin is present in the intact garlic clove. The garlic plant produces allicin as a natural defense against bacteria and other organisms. Allicin is highly irritating and has been shown to be bactericidal in in vitro studies." (See Alternative Medicine Alert, September 1998, pp. 97-99.)
A review of the literature revealed numerous laboratory studies demonstrating antifungal activity8-14 as well as antibacterial activity.1 Several reports on the effectiveness of garlic in humans were also found.15-17
For example, researchers in Japan studied the antifungal properties of garlic by taking a garlic extract obtained from crushed cloves and applying it to agar mediums inoculated with different fungi of clinical importance.8 The extract, containing allicin, was highly effective against Candida, Cryptococcus, Trichophyton, Epidermophyton, Microsporum, and less so against Aspergillus. Allicin was found to inhibit both germination of spores and growth of hyphae.
The effect of garlic on Cryptococcus also has been reported.9 In China, when given intravenously, garlic extracts reportedly have been used with success in the treatment of cryptococcal meningitis.10 Researchers in New Mexico obtained and studied this Chinese extract, i.e., diallyl trisulfide or allitridium, and found it to contain properties for in vitro killing against C. neoformans and to work synergistically with amphotericin B.
Other researchers have taken fungal isolates from clinical cases and have tested garlic extracts’ antifungal ability. For example, of 88 isolates of dermatophytes from cases of tinea capitis, tinea corporis, and tinea cruris, 76 were sensitive to a garlic extract at a dilution of 1:150 and all at 1:100.11 In comparison, when the isolates were tested with ketoconazole, 71 were sensitive at a concentration of 1 mcg/mL and all at 5 mcg/mL. Similarly, 22 cultures of C. albicans isolated from active vaginal yeast infections were tested for sensitivity to garlic extract.12 The garlic extract was found consistently to inhibit the growth of C. albicans.
The effect of garlic extracts on otomycosis has also been studied.13 Otomycosis is a common condition seen in pediatric practice. Researchers at the University of New Mexico compared the antifungal properties of aqueous garlic extract (AGE) and concentrated garlic oil (CGO) with three commercial preparations commonly used in practice, i.e., cresylate otic solution, Lotrimin, and ketoconazole cream. Using agar disks inoculated with the fungi, the authors demonstrated a dose response of both garlic extracts against the three dermatophytes studied, i.e., Aspergillus fumigatus, A. niger, and A. terreus. When compared to the commercial products, CGO was found to have greater inhibitory activity than the three antifungal agents. AGE had less activity than Lotrimin but greater activity than cresylate and equal activity to ketoconazole cream. In the treatment of keratomycosis, however, other researchers failed to demonstrate an effect of garlic extract.14
Thus, garlic extracts have been demonstrated to be effective against a wide variety of fungi, including fungi isolated from clinical cases, and have been shown to be as effective in vitro as conventional therapeutic agents for otomycosis. In addition to lab studies on fungi, a Boston study demonstrated a broad spectrum of activity of garlic extracts against gram-positive and gram-negative organisms.1 The authors also used an extract that was 40% concentrated.
Unfortunately, there have not been any well-controlled trials in humans. There are, however, several case reports and one case series in which the therapeutic effect of garlic has been studied. One case report involved a culture confirmed lesion of Microsporum canis on the arms of a young women.15 Freshly cut garlic was applied to the lesions on one arm and tolnaftate to the lesions on the other arm. The arm treated with garlic took 10 days to heal; the other took four weeks. Another case report cites the successful treatment of culture-confirmed sporotrichosis.16 The patient was monitored for six months and had no recurrence.
Clinicians in Venezuela reported on the efficacy of a garlic extract, such as ajoene, in the treatment of culture-confirmed tinea pedis in 34 soldiers living in conditions that favored dermatophytosis, i.e., humid conditions and occlusive foot wear.17 On the seventh day of treatment, 27 of the 34 had no clinical signs, and cultures taken immediately and one week later were negative. The remaining seven soldiers were treated for an additional seven days with success. All 34 soldiers were culture negative at 90 days.
Raw garlic may be caustic to the skin. Several cases of dermatitis following the topical application of sliced garlic cloves have been reported.2,18 Raw garlic can also cause stomach upset, reflux and GI upset. If this should occur it would indicate the need to stop treatment and re-evaluate.
Garlic taken internally may potentiate the effects of anticoagulants, antihypertensives, and antidiabetic agents.19 Garlic may have antithrombotic activity so it is not recommended for patients taking anticoagulants.20
Many companies promote preparations containing garlic. Some come as oil, some as capsules, some as dried powders, some as extracts. Internal and external preparations are used for topical infections; topical is preferred.
Topically, sliced cloves or commercial garlic oil is applied two to three times a day. Lesions may need to be treated for one to two weeks. The usual dose for internal administration of allicin extracts is 2-5 mg per day.
Medicinal preparations of garlic have existed for thousands of years. Garlic has a strong history as a remedy for skin infections, particularly for fungus. Numerous laboratory-based studies have demonstrated a significant fungicidal effect of garlic extracts. Importantly, this effect has been demonstrated on multiple isolates obtained from clinical cases. Data from human studies are limited but suggest a positive antifungal effect.
When questioned by their patients about garlic, clinicians could advise that laboratory studies suggest both fungicidal and bactericidal effects. Although clinical studies are limited in number and in scope, they do suggest potential benefit in the treatment of fungal infections. Clinicians should advise their patients that if used as an external remedy, the patient should observe for the development of contact dermatitis which, on rare occasion, has been reported.
1. Farbman KS, et al. Antibacterial activity of garlic and onions: A historical perspective. Pediatr Infect Dis J 1993;12:613-614.
2. Garty BZ. Garlic burns. Pediatrics 1993;91:658-659.
3. Blumenthal M, et al. eds. The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicine. 1st ed. Austin, TX: American Botanical Council; 1998.
4. Gruenwald J, et al. eds. PDR for Herbal Medicines. 1st ed. Montvale, NJ: Medical Economic Company; 1998.
5. Lun ZR, et al. Antiparasitic activity of diallyl trisulfide (Dasuansu) on human and animal pathogenic protozoa (Trypanosoma sp., Entamoeba histolytica and Giardia lamblia) in vitro. Ann Soc Belg Med Trop 1994;74: 51-59.
6. Weber ND, et al. In vitro virucidal effects of Allium sativum (garlic) extract and compounds. Planta Med 1992;58:417-423.
7. Lau BH, et al. Garlic compounds modulate macrophage and T-lymphocyte functions. Mol Biother 1991;3:103-107.
8. Yamada Y, Azuma K. Evaluation of the in vitro antifungal activity of allicin. Antimicrob Agents Chemother 1977;11:743-749.
9. Fromtling RA, Bulmer GS. In vitro effect of aqueous extract of garlic (Allium sativum) on the growth and viability of Cryptococcus neoformans. Mycologia 1978;70:397-405.
10. Shen J, et al. Enhanced diallyl trisulfide has in vitro synergy with amphotericin B against Cryptococcus neoformans. Planta Medi 1996;62:415-418.
11. Venugopal PV, Venugopal TV. Antidermatophytic activity of garlic (Allium sativum) in vitro. Int J Dermatol 1995;34:278-279.
12. Moore GS, Atkins RD. The fungicidal and fungistatic effects of an aqueous garlic extract on medically important yeast-like fungi. Mycologia 1977;69:341-348.
13. Pai ST, Platt MW. Antifungal effects of Allium sativum (garlic) extract against the Aspergillus species involved in otomycosis. Lett Appl Microbiol 1995;20: 14-18.
14. Mahajan VM. Antimycotic activity of different chemicals, chaksine iodide and garlic. Mykosen 1983;26: 94-99.
15. Rich GE. Garlic an antibiotic? Med J Aust 1982;1:60.
16. Tutakne MA, et al. Sporotrichosis treated with garlic juice. A case report. Indian J Dermatol 1983;28:41-45.
17. Ledezma E, et al. Efficacy of ajoene, an organosulphur derived from garlic, in the short-term therapy of tinea pedis. Mycoses 1996;39:393-395.
18. Lee TY, Lam TH. Contact dermatitis due to topical treatment with garlic in Hong Kong. Contact Dermatitis 1991;24:193-196.
19. Cirigliano M, Sun AY. Herbal Medicine: What Works, What’s Safe: An Overview. In: The Physician’s Guide to Alternative Medicine. Atlanta, GA: American Health Consultants; 1999:13-20.
20. Schulz V, et al. Rational Phytotherapy, 3rd ed. New York: Springer-Verlag; 1998:112.