There are a number of reasons why you may need to wash your dog. They may have graced your house with a fragrant roll in fox or badger poo, you may find that your own allergies reduce with regular dog baths, or the dog may have a skin disease requiring medicated shampoo as treatment. There is now a massive range of dog shampoos, but surely a human shampoo, or even soap or washing up liquid would be just as effective?
Unfortunately, although human shampoo will clean the coat and help to remove mud and smells, using human or household products can damage the dog’s skin and lead to skin disease.
The structure of a dog’s skin
The outer layer of the skin (the epidermis) protects the body from organisms such as bacteria, viruses and yeasts which can cause infection if they invade the skin. The epidermis is made up of a number of layers, the outer layer (the stratum corneum) is covered by an ‘acid mantle’. This acid mantle can be damaged by chemicals which have a different acidity level.
When we consider acidity – measured on the pH scale – water is neutral and has a pH of 7. Acids have a pH below 7 and alkaline solutions have a pH above 7. Both acidic and alkaline solutions can cause burns or damage to skin if applied to surfaces with a very different pH. The dog has a skin pH which tends to be neutral or mildly alkaline, around 7-7.5 but human skin has a much more acidic pH, around 5.2- 5.5. Therefore, shampoo designed for human skin, even baby shampoo will be too acidic for dogs’ skin and can damage the surface of the skin. This damage makes dogs prone to skin infection.
Below the acid mantle lies the stratum corneum. This is a porous layer that protects the rest of the epidermis from drying out, as well as sloughing off any dangerous microorganisms and allergens. It is made up of layers of dying cells, in the dog it is 8-10 cells thick across most of the body, half as thick as the human stratum corneum.
The impact of bathing
Bathing strips away the acid mantle. If the acid mantle is disrupted, the stratum corneum is unprotected. As it dries out the skin becomes red, irritated, flaky and dry leading to itching, rashes and infection. Human shampoos often contain moisturisers to replace the protective layer which is washed away, but as the acidic pH disrupts the acid mantle and dries out the stratum corneum of the dog, they will not be absorbed into canine skin, and so do not prevent the damage and subsequent infection that can occur.
Skin infections can make dogs smell, but then repeated washing may make this worse as there is increased disruption to the protective layers of the skin. In this and most cases, shampoos should be carefully chosen to protect the skin, with a pH of around 7. Moisturisers which can be absorbed by canine skin are important and artificial colours or fragrances should be minimised. Water alone can be used to bathe dogs who have debris in their coat.
What about allergies?
Dogs with allergies have been shown to have an altered skin structure which makes them prone to skin damage. Shampoo choice is especially important in maintaining the hydration and fatty acid levels in these dogs. If a dog produces too much oil as a result of the skin being damaged, either by shampoo or other insults, the skin becomes thick and oily and less effective at preventing infection. Because of this, and the fact that the epidermis protects the skin from UV light damage, damage with inappropriate shampoo can lead to severe skin disease.
Although dog shampoo maybe expensive and seem extravagant, it really does prevent damage to their skin, and skin disease! If your dog seems to need very regular washing or bathing, is unusually smelly, or has red, inflamed, sore or itchy skin, do seek veterinary advice – skin infections and other conditions are much easier to manage if diagnosed and treated