Karen Helton Rhodes, DVM, DACVD Terri Bonenberger, DVM, DACVD
Topical Ingredients: what is really effective? (Oatmeal dog shampoo, Tea Tree oil, etc)
There are a number of topical products on the market (creams, lotions, shampoos, mousse, rinse, sprays, etc) and many, if not most, of them promise miraculous cures. The same is true for both veterinary and human products. Don’t forget those wrinkle creams that will make you look 20 years younger in only one month! Veterinary topical products can also fall prey to wild promises. It is prudent to be an educated consumer and understand what an ingredient can and cannot contribute to a formula. Unfortunately, many companies do not feel the need to be entirely honest with the consumer. They prey on your frustration and needs by promoting false recommendations. As a consumer you should evaluate the validity of a topical product by reading the ingredient list to see if there is the potential for that product to deliver what the company claims. For example; an oatmeal dog shampoo might promise to be anti-itching or soothing. Find out if that is true! Read below to explore individual ingredients and their clinical benefit for your dog.
INTRODUCTION: The skin is a dynamic organ. It actually regenerates itself every 3-4 weeks. Thus the reason our suntans never last! It is actually of great benefit for the skin to rebuild itself since the skin is constantly under barrage from the environment. Keeping the haircoat free of dirt, debris and mats allows for appropriate thermoregulation and discourages bacterial and yeast overgrowth.
The skin requires certain “structural components” for normal health balance. Many skin diseases disrupt this balance and perpetuate the problem. Allergic patients are an excellent example in that the epidermal lipid barrier is disrupted in allergic dogs (as well as people). This barrier is necessary to prevent allergen exposure and helps avoid secondary infections. Allergy patients are at risk due, in part, to this defective barrier. I think the best way to look at ingredients is to group them by mode of action. This discussion will include only those ingredients with scientific documentation of efficacy for the sake of brevity. Future blogs will address other “popular or trending” ingredients.
1. pH, temperature, hydration: Although pH is not an ingredient, pH is vitally important to the homeostasis of the skin. Some shampoos have a pH balanced for human skin, which is more acidic that dog skin. Human pH-balanced shampoos are not optimal for the dog as they may alter the electrostatic charges in the surface lipid bilayer of the epidermal surface lipid bilayer (remember, this barrier is important in allergy skin!) and could thus alter the barrier effect which protect the skin. Temperature and hydration of the skin can influence how an ingredient reacts on/in the skin. Hydration is probably the most important factor. In general, the skin is much more permeable when hydrated. That fact is why you should always apply body creams or oils after a shower for maximum benefit. Your dog’s skin is no different. The “old wives tale” that frequent bathing is harmful is so very wrong!
2. Emollients or moisturizers: Emollients (safflower, sesame, mineral oils, lanolin, beeswax) soften, lubricate and soothe the skin- they should be applied immediately after bathing or saturation of the skin with water to retain hydration. Moisturizers (propylene glycol, glycerin, colloidal oatmeal, urea, sodium lactate, carboxylic acid and lactic acid) increase the water content of the outer layer of the skin. These agents work by being incorporated into the outer layer of the skin and attracting water.
3. Antipruritics (anti-itching): These ingredients attempt to provide relief from itchy skin. There are a number of causes of itchy skin so any one particular ingredient is not likely to alleviate discomfort in every dog. Providing epidermal lipid barrier repair (ceramides) may help allergy patients. Antibacterial ingredients (NaHypochorite, benzoyl peroxide, or chlorhexidine) may help those dogs with bacterial or yeast infections. So, you can see that the actual disorder is important when choosing a topical product! Anti-itching ingredients typically work via a variety of different methods: 1) removing surface irritants or allergens (NaHypochlorite, chlorhexidine), 2) substituting another sensation such as heat or cold (ex- menthol or camphor), 3) anesthetizing the peripheral nerves (pramoxine, lidocaine, benzocaine, etc), 4) raising the “itch threshold” by cooling or moisturizing the skin (essential fatty acids-EFAs , glycerin, urea, oatmeal). Remember, dry skin is itchy skin so you typically want to avoid astringents. 5) repairing the epidermal lipid barrier (ceramides, Vitamin E, allantoin, and EFAs), and 6) biochemical agents such as steroids or antihistamines.
Note this pictorial of the epidermal skin barrier has an orderly layer effect.
4. Antimicrobial (antibacterial and anti-yeast) agents: Anytime the skin is damaged or abnormal (altered barrier) bacteria and yeast take advantage of the situation and overgrow causing infection. There are a large number of antimicrobial ingredients. The emergence of resistant bacterial strains (MRSA, MRSP, etc) has made the use of antimicrobial topical vitally important. Some of the topicals have also begun to be less effective while others have continued to be excellent choices.
Sodium hypochlorite (NaHypochlorite) has remained an excellent antibacterial as well as anti-yeast ingredient. In fact, if you are diagnosed with a MRSA (methicillin resistant Staphylococcus aureus) infection, our physician will recommend bleach baths! They are highly effective, even over and above some of the more conventional ingredients such as chlorhexidine or iodines. As such, this ingredient has become an important weapon against staph infections in both dogs and people. Benzoyle peroxide is another antibacterial ingredient but it can be drying and thus sometimes irritating for allergy patients. Think of the irritation that is noted in some people with the use of acne medications that contain this ingredient. The same holds true in the dog. Tea Tree Oil(Melaleuca oil) has been shown to have proven yet limited antibacterial and fungicidal properties. Exercise caution since an inappropriate or excessive use of tea tree oil on the skin can cause drooling, incoordination, weakness, low body temperature, and liver damage.
5. Astringents: These ingredients must be used with caution as they cause cause drying of the skin and perpetuate itching. They are best used for acute moist focal areas like direct application to a “hot spot”. They include: tannic acid, witch hazel, aluminum acetate (Burow’s solution), acetic acid or vinegar, silver nitrate solution, or potassium permanganate solution.
6. Antiseborrheics: These ingredients are best for dogs with a scaling skin disease or even ones that tend have exceptionally oily skin. Fatty acids can be helpful in these cases as they are often keratolytic (break down scale). Urea is another ingredient that can help remove scale. Urea is most often used in a cream or ointment formulation for application to the nose or footpads. Salicylic acid is helpful for both antimicrobial control as well as decreasing scaling.