Bacteria, viruses, and fungi may not only cause primary infections of the skin like warts, herpes, folliculitis, onychomycosis, erysipelas, and many more but also complicate existing dermatological disorders like oozing eczema or intertrigo. Three factors suggest that infec- tions of the skin will remain important in the future: increased mobility with dispersal of microorganisms across the world, susceptibility of the skin because of intensive hygiene, and development of resistant strains, for example, in Staphylococcus aureus. Plant extracts, juices, and decoctions have always been used to treat infections of the skin.
Bacterial infections: Numerous botanical compounds exhibit antimicrobial activities in
vitro. Usually, antiseptic or antibiotic treatment is still the treatment of choice, and plant- derived antimicrobial therapeutics are rather used in an adjuvant manner or in mild cases of bacterial infections. For example, tea tree oil (Melaleuca alternifolia; TTO) not only is benefi cial in the topical therapy of acne as mentioned before. It also functions as a topical antiseptic with an effi cacy superior to that of phenol and displays broad- spectrum antimicro- bial activity in vitro against gram- negative bacteria such as Escherichia coli, gram- positive bacteria such as Staphylococcus aureus, and the yeast Candida albicans (63) [LOE- D]. Disruption of plasma membrane barriers for ions and small molecules is discussed as a mode of action, monoterpenes being the active compounds.
Hyperforin, a major compound from St. John’s wort (Hypericum perforatum), has been demonstrated to be highly effective against a panel of gram- positive bacteria, including multiresistant Staphylococcus aureus (10) [LOE- D].
Coriander oil (Coriandrum sativum) is another topical plant- derived agent with distinct antibacterial effi cacy and good skin tolerance (32) [LOE- D]. It has been shown to be highly effective against Escherichia coli and other bacteria and fungi in vitro (64– 68) [LOE- D]. Some isolated compounds (long-chain alcohols and aldehydes) may be very effective, but their combined effects in the crude oils are diffi cult to predict. Dodecenal from coriander had a minimum bactericidal concentration of 6.25 μg/ml against Salmonella choleraesius (68). Strength and spectrum of coriander oil fractions often exceeded those determined in the crude oil, but mixing of single fractions could result in additive, synergistic, or antago- nistic effects. Recently, a topical lipolotio containing 1% v/v coriander oil has also been shown to inhibit UVB- induced erythema in humans to a signifi cantly higher extent com- pared to placebo but less than 1% hydrocortisone (69) [LOE- A], making coriander oil an interesting treatment for infl ammatory skin diseases with bacterial colonization.
Various plant extracts and isolated compounds have been screened for antimicrobial ef- fects on bacteria and yeasts with dermatological relevance. Plant extracts from olibanum (Boswellia serrata), rosemary (Rosmarinus offi cinalis), sage (Salvia offi cinalis), and others have been shown to inhibit the growth of several gram- positive bacteria such as Staphylococ-
cus aureus (including methicillin- resistant strains), Propionibacterium acnes, and Coryne- bacterium species (52) [LOE- D].
Japa nese Kampo formulations have also been shown to possess antibacterial properties directed toward Propionibacterium acnes, Staphylococcus epidermidis, and Staphylococ-
cus aureus (70) [LOE- D].
Fungal infections: Numerous botanicals, especially essential oils, exhibit antifungal ac-
tivities in vitro. The essential oil of snow gum (Eucalyptus paucifl ora) has been shown to pos- sess strong antifungal properties against a broad spectrum of human pathogenic fungi, including Epidermophyton, Microsporum, and Trichophyton species. Within a non-vehicle- controlled clinical study, 1% essential oil formulated into an ointment was applied topically twice a day for three weeks to 50 patients suffering from tinea pedis, tinea corporis, or tinea cruris. After the second week of treatment, all patients were negative for fungal infection confi rmed by microscopic evaluation of the scraping from the infected area after staining with 10% potassium hydroxide (KOH). After three weeks of treatment, 60% of the patients recovered completely as proven by microscopic evaluation and clinical signs such as erythema, scaling, itching, maceration, vesiculation, and pustulation, and 40% of the patients showed signifi cant improvement of the clinical signs of tinea without any adverse effects. No KOH- negative cases relapsed at reexamination of the patients two months after the end of the treatment (71) [LOE- B].
Another antifungal plant is garlic (Allium sativum). Garlic contains the biologically active ingredient ajoene, a trisulphur compound that has been demonstrated to possess antifungal properties. In a clinical study with 34 patients suffering from tinea pedis, the use of an 0.4% ajoene cream resulted in complete clinical and mycological cure in 79% of the patients af- ter seven days of treatment. The remaining 21% of patients achieved complete healing after seven additional days of treatment. All patients were evaluated for recurrence of my- cotic infections 90 days after the end of treatment, yielding negative mycological cultures (72) [LOE- B].
Viral infections: Numerous botanicals exhibit antiviral properties in vitro. Only a few
have been studied in vivo so far. Lemon balm (Melissa offi cinalis) formulated into a cream was investigated in a double- blind, placebo- controlled, randomized trial in 66 patients with recurrent herpes simplex labialis. The cream was used four times daily over a period of fi ve days on the affected area. Lemon balm treatment resulted in signifi cantly faster healing time and reduced spread of infection, blistering, and pain compared to placebo (73) [LOE- A].
A well- established dermatological therapy of Condylomata acuminata, which are caused by human papilloma viruses, is podophyllotoxin, extracted from the root of American may- apple (Podophyllum peltatum). Recently, in a randomized, double- blind study, 97 patients suffering from recurrent condylomata acuminata were treated with a podophyllotoxin solid lipid nanoparticles gel and a standard podophyllotoxin gel. The condyloma clearance rate in patients receiving podophyllotoxin solid lipid nanoparticle gel was 97.1%, close to that for patients treated with the routine preparation of 90.6%, but the nanoparticle preparation signifi cantly reduced the recurrence rate and adverse side effects. It was concluded that podophyllotoxin delivered via solid lipid nanoparticle gel can effectively clear Condylomata
acuminata and reduce the recurrence rate with only mild, tolerable side effects (74)
[LOE- A].
An extract of arbor vitae (Thuja occidentalis) in the form of a tincture has traditionally been used as a topical treatment for common warts (Verrucae vulgares). Similarly, the ap- plication of fresh juice from greater celandine (Chelidonium majus) is said to be benefi cial in the treatment of warts (52) [LOE- D]. Traditional systemic botanical treatment of warts includes immunostimulating plant extracts from purple conefl owers (Echinacea purpurea) or Siberian ginseng (Eleutherococcus senticosus) administered orally over a period of eight weeks (52) [LOE- D]. However, the effi cacy of these traditional therapies has not been proven in controlled clinical trials so far.
In summary, there are effective botanicals for topical treatment of bacterial, fungal, and viral infections of the skin. They can be used adjuvant to other therapeutical mea sures or alone in mild to moderate cases. Especially when essential oils are used, possible contact sensitizations should be kept in mind. An important aspect is that garlic or aromatic herbs may be available when modern medicine is not, and this applies not only to the Third World but also to catastrophes in industrial nations, as we are experiencing them again and again. Some of these treatments are old house remedies that should not be forgotten.