The Skinny on Herbs for the Skin
By Narda Robinson, DO, DVM
A dizzying display of botanical products confronts shoppers scanning pet store aisles and natural pet magazines to find safe and effective alternatives for their dogs’ itchy, painful skin.1 The under-enforcement of federal regulations has given a green light to unfettered expansion of unproven cures. Consumers try their best to navigate the maze of claims and testimonials, left in the dark as to whether a product will help or harm their animals.
The sheer number of botanical creams, ointments and lotions crammed on supplement shelves can cause canine caregivers to scratch their heads in confusion.
Isn’t anyone minding the store when it comes to stocking herbal potions?
Why do animal skin-care products still contain chaparral and comfrey when their well-publicized pyrrolizidine alkaloids are likely to end up ingested by an auto- or allo-groomer?2
How do companies reconcile the ethical issues involved in selling goldenseal and other endangered plants suffering from overharvesting and habitat elimination? Where is the appropriate labeling on potentially toxic essential oils?3
Even products for humans can be unsafe, as illustrated by Chinese so-called “herbal” skin creams that have been purposefully adulterated by manufacturers with undisclosed steroids to make them work better.4 In addition to hiding undisclosed pharmaceuticals, the herbs themselves can pose hazards of intrinsic toxicity, microorganisms, microbial toxins, fumigation agents, heavy metals, animal substances, insect parts, worms and pesticides.5
Anti-oxidants and Anti-cancer
Drawbacks of Chinese mystery mixtures aside, research has shown that a number of plant-based agents do actually benefit the skin when applied topically.6,7,8
Many confer anti-oxidant activity, including soy, mushroom extracts, tea, feverfew and polypodium, suggesting potential value for cancer prevention.9 Silymarin, from milk thistle, possesses naturally occurring polyphenolic flavonoids; these may deliver anti-carcinogenic activity.
Furthermore, curcumin (the key active component of turmeric), when directly applied in a cream or salve, may inhibit the initiation and promotion of tumorigenesis. It exhibits strong potential as a topical agent for wound repair, especially issues caused by radiation.
Anti-infective
Tea tree oil, an essential oil with concentrated chemical constituents, has become popular for its anti-microbial value. By blocking the conversion of the yeast form of Candida albicans to its pathogenic mycelial counterpart, tea tree oil demonstrates anti-fungal activity. It may also alleviate the edema associated with contact allergy and control histamine-induced edema linked to type I hypersensitivity reactions. A drawback for veterinary usage is its toxicity for small animals when applied in large amounts. It also should not be used on burns because it can be cytolytic to epithelial cells and fibroblasts.10
Anti-inflammatory and Reparative
Arnica is frequently found in products designated for traumatic and inflammatory skin conditions. It reduces inflammation through its inhibition of the transcription factor nuclear factor kappa B, whose role it is to transcribe genes that produce pro-inflammatory mediators. Arnica also inhibits genes responsible for antigen presentation and COX-2. Problems with arnica include the risk of producing contact dermatitis; it should be avoided on open wounds or broken skin. Arnica is now a protected species due to over harvesting and reduction of natural habitat.
Bromelain, a proteolytic enzyme derived from pineapple stems, limits inflammation, edema and pain. In so doing, it may accelerate healing after trauma and surgery. German chamomile improves skin texture and elasticity, reduces pruritus and can shorten the healing time for wounds. Pomegranate, widely recognized for its strong anti-oxidant activity, may foster skin regeneration through agents derived from the peel and seeds. Ginseng-derived ginsenosides yield properties that promote wound healing, hair regrowth and treat pruritus.
Grape seed extract (GSE) promotes expression of vascular endothelial growth factor (VEGF) in keratinocytes; it may foster angiogenesis in wounds and benefit animals struggling with recalcitrant lesions. Topical application in experimental wounds produced in mice showed that grape seed proanthocyanidin extract sped wound contraction and closure, enhanced BEGF and tenascin expression at the wound edges, and produced better connective tissue deposition with higher cell density.11
Aloe vera leaves produce a gel well known for healing wounds and burns.12 Beyond this effect, aloe gel accelerates recovery from chronic leg ulcers in humans and surgical wounds. It aids patients with frostbite by augmenting dermal perfusion. Aloe’s analgesic effects may stem from the carboxypeptidase content in its leaves. This enzyme inactivates bradykinin, a nociceptive compound that accompanies inflammation. Anti-inflammatory benefits of aloe relate to its salicylic acid and magnesium lactate content. Aloe can, however, cause contact dermatitis.
Marigold (calendula) likewise benefits patients recovering from ulcers, burns, rashes and wounds. Marigold, often found as a calendula gel, stimulates granulation and increases collagen and glycoprotein content in areas of broken skin.13
Licorice extract possesses anti-inflammatory properties; animal models given Glycyrrhiza glabra extract demonstrated that licorice provides anti-mutagenic, anti-carcinogenic and tumor suppressive effects. Rosemary, too, has anticancer, anti-inflammatory and antimicrobial value. However, all this biological activity comes at a price; i.e., the risk of contact dermatitis. Lavender, commonly found in soaps and shampoos, has skin soothing properties; its tannins may help reduce oozing and bleeding in open sores.14 However, like rosemary, it may provoke contact allergy.
Anti-itch
Colloidal oatmeal suspensions have a long-standing reputation for treating pruritus, even in burn victims. It has the added advantage of helping to protect and repair skin and hair damaged by smoke, bacteria, UV radiation, and free radicals.
Topical’s ‘Dark Side’
Nearly any herb may cause cutaneous reactions, the most common related to allergic contact dermatitis.15,16 More serious dermatologic reactions documented in humans include generalized exfoliative dermatitis, erythema multiforme, and bullous and nodular lichen planus. Topical botanicals, like ingested ones, can help or harm, depending on the individual, the components of the mixture and product purity.
In the absence of methodologically sound clinical trials on target species with naturally occurring disease, a process of trial and error may be the only option.
Caregivers should look for products listing relatively safe ingredients and remain vigilant for untoward outcomes.
Dr. Robinson, Dipl. ABMA, FAAMA, oversees complementary veterinary education at Colorado State University.
FOOTNOTES
1. Tilford GL. Herbal remedies for your dog’s chronic skin inflammation. The Whole Dog Journal. May 2004. Accessed here on 10-30-11.
2. Buchness MR. Alternative medicine and dermatology. Seminars in Cutaneous Medicine and Surgery. 1998;17(4):284-290.
3. Villar D, Knight MJ, Hansen SR, et al. Toxicity of melaleuca oil and related essential oils applied topically on dogs and cats. Veterinary and Human Toxicology. 1994;36(2):139-142.
4. Keane FM, Munn SE, du Vivier AWP, et al. Analysis of Chinese herbal creams prescribed for dermatological conditions. Western Journal of Medicine. 1999;170(5):257-259.
5. Koh H-W and Woo S-O. Chinese proprietary medicine in Singapore. Regulatory control of toxic heavy metals and undeclared drugs. Drug Safety. 2000; 23(5):351-362.
6.Baumann L. Botanical ingredients in cosmeceuticals. Journal of Drugs in Dermatology. 2007;6(11):1084-1088
7. Baumann LS. Less-known botanical cosmeceuticals. Dermatologic Therapy. 2007;20:330-342.
8.Bedi MK and Shenefelt PD. Herbal therapy in dermatology. Arch Dermatol. 2002;138:232-242.
9.Berson D. Natural antioxidants. Journal of Drugs in Dermatology. 2008;7(7supp):s7-s12.
10. Bedi MK and Shenefelt PD. Herbal therapy in dermatology. Arch Dermatol. 2002;138:232-242.
11.Khanna S, Venojarvi M, Roy S, et al. Dermal wound healing properties of redox-active grape seed proanthocyanidins. Free Radic Biol Med. 2002;33:1089-1096.
12.Bedi MK and Shenefelt PD. Herbal therapy in dermatology. Arch Dermatol. 2002;138:232-242.
13.Bedi MK and Shenefelt PD. Herbal therapy in dermatology. Arch Dermatol. 2002;138:232-242.
14.Bedi MK and Shenefelt PD. Herbal therapy in dermatology. Arch Dermatol. 2002;138:232-242.
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