Shampoo therapy: making sense of all of the choices (Proceedings)

May 01, 2011

Shampoo therapy is an important adjuvant therapy in pets for treating a variety of dermatologic conditions. In order to get the maximum benefit of the shampoos, the shampoos need to be used properly. Contact time is of utmost importance when using shampoos. The shampoo needs to be on contact of the skin for 5 to 15 minutes. The contact time allows for proper hydration of the skin but provides sufficient time for the penetration and action of the shampoo ingredients. It is also important that shampoo be thoroughly rinsed off so that no residual shampoo is present which could irritate the skin.

Pet owners prefer a shampoo that smells and lathers well. Therefore, if you have a choice between two shampoos with similar ingredients then it may be best to purchase the shampoo that has a more pleasant smell and one that lathers well.

Depending on the condition being treated, some pets require twice weekly until adequate control of odor, grease and scale are achieved (usually 2 to 4 weeks worth of therapy). After that time, depending on the individual's response to the shampoo therapy, a maintenance shampoo as frequently as once weekly or as little as once monthly may be required. It is important to realize that the maintenance shampoo therapy may need to be adjusted depending on seasonal influences (i.e. variations in heat, humidity) since changes in environmental influences can affect dryness, greasiness, scaliness and the tendency to develop bacterial infections.

One question that is often asked by pet owners is whether they can use their human shampoo to bathe their pet. Several differences exist between human skin and dog and cat skin. The human epidermis is 10 to 15 layers thick and normally displaces a 28 day transit time from the basal to cornified layer. This differs from dogs that have 3 to 5 cell layers and the cat has 1 to 3 cell layers of the epidermis. The skin turnover time for pets is 1 week which is a much shorter time period than humans. The pH also differs between humans and dogs and cats. The pH of human skin is acidic 5.5 whereas dog and cat skin pH is neutral or 7.5. Therefore, bathing with a human shampoo in pets would decrease the surface pH of the skin which would result in potential skin irritation, drying, scaling and changes in the bacterial flora on the skin.

Currently over 100 veterinary shampoos exist. Instead of memorizing all of the different shampoo name brand options, a more logical approach is to become familiar with the active ingredients in shampoos and become educated in their clinical applications and any side effects associated with their use. The different shampoo types to be discussed are moisturizing shampoos, antipruritic, antibacterial shampoos, antifungal shampoos and antiseborrheic agents.

Moisturizing ingredients

Two different types of moisturizing ingredients exist for shampoos and other topical products. These two ingredients are emollients and humectants. Examples of emollients are oils (i.e. almond, corn, cotton seed, coconut, olive, peanut, Persia, safflower and sesame), animal fats (i.e. lanolin) and hydrocarbons (i.e. mineral oil, paraffin, petrolatum). Examples of humectants include: natural moisturizing factors (i.e. carboxylic acid, lactic acid, urea), sodium lactate, propylene glycol, glycerin, and polyvinylpyrrolidone.

Both of these ingredients may accomplish the same objective of moisturizing the skin but they work differently. The emollients moisturize the skin by supplying a layer of oil to coat the skin. The humectants work by drawing the moisture up out of the skin to rehydrate outer surface of the skin.

Antipruritic ingredients

Three ingredients have been added to shampoos because of their antipruritic properties. These three ingredients include: oatmeal, pramoxine and aloe vera. All of these products are safe and have minimal side effects. Although extremely rare and antedoctal, the only reported side effect is skin irritation when aloe is used topically. The way that each of these ingredients differ is by the mechanism of action.

Oatmeal evolved out of folk medication and it has been reported to soothe irritated skin for as long as 2 days. The exact mechanism of action is unknown but it is thought to decrease inflammation of the skin by inhibiting prostaglandins.

Pramoxine is a topical local anesthetic that numbs the skin by decreasing the neuronal membrane's permeability to sodium ions. This decrease in the amount of sodium ions being present on the neuron results in the initiation and conduction of pain impulses being blocked so depolarization of the neuron's impulses are inhibited. Pramoxine starts as quickly as 2 to 5 minutes and lasts for several days.

Aloe vera is from stabilized viscous juice from the inner part of the aloe vera leaves. The two chemical components of aloe vera that produce its antipruritic effects are salicylic acid and magnesium lactate. Salicylic acid inhibits the production of prostaglandin from arachidonic acid by inhibiting cyclooxygenase. The magnesium lactate inhibits the conversion of histidine to histamine in mast cells by an enzyme called histidine carboxylase. Aloe vera also products healing properties by increasing dermal perfusion and decreasing inflammatory mediators (i.e. thromboxane, prostaglandin) in burn lesions. Side effects of aloe vera in pets have not been reported.