Botanicals in Dermatology: An Evidence-based Review

Juliane Reuter; Irmgard Merfort; Christoph M. Schempp

Disclosures

Am J Clin Dermatol. 2010;11(4):247-267. 

In This Article

3. Infectious Skin Diseases

3.1 Bacterial Infections

Numerous botanical compounds exhibit antimicrobial activities against microbes with dermatologic relevance in vitro. However, the clinical evidence for their efficacy is poor and, therefore, antiseptic, antimycotic or antibacterial treatment using synthetic compounds is still the treatment of choice. Plant-derived antimicrobial therapeutics are used in an adjuvant manner or in mild cases of bacterial infections. For example, tea tree oil (M. alternifolia) is not only effective in the topical therapy of acne as mentioned in section 1. It functions as a topical antiseptic with an efficacy superior to that of phenol and displays broad-spectrum antimicrobial activity in vitro against Gramnegative bacteria such as Escherichia coli, Gram-positive bacteria such as Staphylococcus aureus, and also against the yeast Candida albicans[69] [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 (H. perforatum), is highly effective against a panel of Gram-positive bacteria, including multi-resistant S. aureus strains[47] [LOE-D].

Coriander oil (Coriandrum sativum) is another topical plant-derived agent with distinct antibacterial efficacy and good skin tolerance[52] [LOE-D]. It is highly effective against E. coli and other bacteria and fungi in vitro[70–74] [LOE-D]. Some isolated compounds (long chain alcohols and aldehydes) may be very effective, but their combined effects in the crude oils are difficult to predict. Dodecenal from coriander had a minimum bactericidal concentration of 6.25 μg/mL against Salmonella choleraesius.[74] The 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 antagonistic effects.

Recently, a topical lipolotion containing coriander oil 0.5% has also been shown to inhibit UVB-induced erythema in humans to a significantly greater extent than placebo, but less than hydrocortisone 1%[75] [LOE-A], making it an interesting treatment for inflammatory skin diseases with bacterial colonization.

Various plant extracts and isolated compounds have been screened for antimicrobial effects on bacteria and yeasts with dermatologic relevance. Olibanum (Boswellia serrata), beard lichen (U. barbata), rosemary (Rosmarinus officinalis), sage (Salvia officinalis), and others inhibit the growth of several Gram-positive bacteria such as S. aureus (including methicillin-resistant strains), P. acnes, and Corynebacterium spp.[12] [LOE-D]. Japanese Kampo formulations also possess antibacterial properties directed towards P. acnes, Staphylococcus epidermidis, and S. aureus[76] [LOE-D].

3.2 Fungal Infections

Numerous botanicals, especially essential oils, exhibit anti-fungal activities in vitro. The essential oil of snow gum (Eucalyptus pauciflora) has been shown to possess strong anti-fungal properties against a broad spectrum of human pathogenic fungi includingEpidermophyton,Microsporum, andTrichophyton species. Within a non-vehicle-controlled clinical study, the Eucalyptus pauciflora essential oil formulated into an ointment was applied topically twice a day for 3 weeks to 50 patients with tinea pedis, tinea corporis, or tinea cruris.[77] After the second week of treatment, all patients were negative for fungal infection as was confirmed bymicroscopic evaluation of the scraping from the infected area after staining with 10% potassium hydroxide (KOH). After 3 weeks of treatment, 60%of the patients recovered completely as proven bymicroscopic evaluation and clinical signs such as erythema, scaling, itching, maceration, vesiculation, and pustulation, and the remaining 40% showed significant improvement of the clinical signs of tinea without any adverse effects. No KOH-negative cases had relapsed at re-examination of the patients 2 months after the end of the treatment[77] [LOE-B].

Another traditional antifungal plant is garlic (Alliumsativum). Garlic contains the biologically active ingredient ajoene, a trisulfur compound that has been demonstrated to possess antifungal properties. In an uncontrolled clinical study of 34 patients with tinea pedis, the use of an ajoene 0.4% cream resulted in a complete clinical and mycologic cure in 79% of the patients after 7 days of treatment.[78] The remaining 21% of patients achieved complete healing after an additional 7 days of treatment. All patients were evaluated for recurrence of mycotic infections 90 days after the end of treatment, yielding negative mycologic cultures[78] [LOE-B].

3.3 Viral Infections

Numerous botanicals exhibit antiviral properties in vitro. Only a few have been studied in vivo so far. Lemon balm (Melissa officinalis) extract formulated into a cream was investigated in a randomized, double-blind, placebo-controlled trial in 66 patients with recurrent herpes simplex labialis.[79] The cream was used four times daily over a period of 5 days on the affected area. Lemon balm treatment resulted in significantly faster healing time, prevented the infection spreading, and relieved blistering and pain better than placebo[79] [LOE-A]. A well established dermatologic therapy of condylomata acuminata, which are caused by human papilloma viruses, is podo-phyllotoxin, extracted from the root of American mayapple (Podophyllum peltatum). Recently, in a randomized, double-blind study, 97 patients with recurrent condylomata acuminata were treated with a podophyllotoxin solid lipid nanoparticle gel and a standard podophyllotoxin gel.[80] The condyloma clearance rate in patients receiving podophyllotoxin solid lipid nanoparticle gel was 97.1%, similar to that with the routine preparation (90.6%), but the nanoparticle preparation significantly reduced the recurrence rate and adverse effects. It was concluded that podophyllotoxin delivered via a solid lipid nanoparticle gel can effectively clear condylomata acuminata and reduce the recurrence rate with only mild, tolerable adverse effects[80] [LOE-A]. Recently, an ointment containing a standardized green tea extract with a high content of epigallocatechin gallate (Polyphenon E_;MitsuiNorin Co. Ltd,Tokyo, Japan) has been shown to be effective in the treatment of condylomata acuminata. To date three randomized, vehiclecontrolled, multicenter clinical studies with 1508 patients have been published. In these studies, patients with external genital or perianal warts were treated with Polyphenon E™ 10% or 15% ointment compared with the vehicle over a period of 16 weeks or until complete clearance. The clearance rates with both Polyphenon E™ concentrations were >50% compared with about 30% with the vehicle. The adverse effects and recurrence rates were low with all treatments.[81,82] [LOE-A].

An extract of arborvitae (Thuja occidentalis) in the form of a tincture has traditionally been used as a topical treatment of common verruca vulgaris. Similarly, the application of fresh juice from greater celandine (Chelidonium majus) is said to be beneficial in the treatment of warts[52] [LOE-D]. Traditional systemic botanical treatment of warts includes immuno-stimulating plant extracts from purple coneflowers (Echinaceapurpurea) or Siberian ginseng (Eleutherococcus senticosus) administered orally over a period of 8 weeks[52] [LOE-D]. However, the efficacy of these traditional therapies has not been proven in controlled clinical trials so far.

3.4 Summary

There are effective botanicals for the topical treatment of bacterial, fungal, and viral infections of the skin. They can be used as adjuvants to other therapeutic measures, 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 does not only apply to the Third World but also to catastrophes in industrial nations, which we are experiencing again and again. Some of these treatments are old household remedies that should not be forgotten.

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