Coat and skin
Human shampoo on dogs: what the pH really changes
Why human shampoo damages a dog's skin, what happens if you have already done it once, and what is actually worth reading on a dog shampoo label instead.
The short answer
No, and the reason comes down to one figure: pH.
Human skin is acidic, it sits around 5.5. A dog's skin is close to neutral, between 7 and 7.5 depending on breed and body area. A shampoo formulated for a pH of 5.5 applied to skin at 7.4 attacks the hydrolipidic film, the greasy layer that holds water in and keeps bacteria at a distance.
The result does not show after the first wash. It shows at the third: dry skin, dandruff, itching, then a dog that scratches and gets infected.
Why a dog's skin copes less well
It is thinner than ours. Its epidermis has three to five layers of cells where ours has around twenty. The barrier is therefore thinner and repairs more slowly.
Dogs do not sweat through the skin. They do not get the same constant acid renewal, which makes the protective film slower to rebuild once it has been stripped.
Another point comes from the fact that a dog swallows whatever you put on its back. The essential oils present in many so-called natural shampoos are poorly tolerated, and tea tree is frankly toxic in dogs as in cats.
What is true in both directions
A one-off wash with human shampoo on a healthy dog is not a disaster. If it has already happened, there is no reason to worry: rinse thoroughly and move on.
Conversely, the pH argument does not make all dog shampoos equivalent. The words "neutral pH" on a bottle mean nothing precise, because a dog's skin varies with the area and the breed, and because no regulation requires the measured value to be stated. A cheap dog shampoo washes, and that is all.
Baby shampoo is not the halfway solution people imagine. It is kind to the eyes, which is a different matter, and it is still set to a human pH.
A healthy dog living indoors does not need a monthly bath. A bath every two to three months is enough in most cases, and a dog that has rolled in something gets rinsed with clean water.
What is worth reading on a label
The real criterion is not the price, it is the reason for washing. A maintenance shampoo, an antiparasitic shampoo and a shampoo prescribed against a skin infection do not do the same job, and the third is not bought in a supermarket.
Be wary of decorative wording. "Natural formula" says nothing about tolerance, and plenty of plants are irritant. "Hypoallergenic" is not a regulated category. What counts is the ingredient list, whether essential oils are present or not, and the stated purpose.
When to see a vet
Itching lasting more than a week. Redness, crusting, a strong smell, weeping areas. Hair loss in patches. A dog chewing its paws down to the skin. These signs are not treated from the shampoo shelf, they need a diagnosis.
Frequently asked questions
I have already washed my dog with my own shampoo, is that serious?
A one-off wash on a healthy dog is not a disaster. Rinse thoroughly and move to a suitable product from now on.
Is baby shampoo a good compromise?
No. It is formulated not to sting the eyes, which is a different matter, and it is still set to a human pH.
Does "neutral pH" on a dog shampoo guarantee anything?
Not much. A dog's skin pH varies with the area of the body and with the breed, and no regulation requires the measured value to be stated.
This article explains and points the way. It is not a diagnosis and is not a substitute for a veterinary consultation. It is published as a preliminary version and will be signed once a veterinary surgeon has approved it.
Also worth reading
Brushing a long-haired cat: the areas everyone forgets
Where the mats actually form on a long-haired cat, why those are the spots nobody brushes, and the one bit of handling that changes the whole session.
Cat losing hair: the test to do before you start worrying
How to tell whether your cat's hair is falling out or whether the cat is breaking it off by licking, and what each of those two cases actually implies.
Dog shampoo pH: why a human product does not suit
A dog's skin sits close to neutral, human skin is acidic. What that one difference actually changes when you are choosing a shampoo bottle off the shelf.
How often to bath a dog: three criteria, not a calendar
Coat type, lifestyle, state of the skin. The three criteria that set how often a dog is bathed, and the signs that tell you to wash him rather less often.
One piece of advice a week
Every Thursday, one subject explained plainly. No advertising, no selling on of addresses.