Why Hypoallergenic Shampoos Don’t Guarantee an Itch-Free Dog

If you have a dog who chews his paws or a cat who grooms too much, then you may be concerned about allergies. In the same way people get hay fever because of pollen in the air, our pets get itchy allergic reactions to substances (allergens) in their environment. This condition that’s common to dogs even has a name: atopy.

But allergies don’t stop there — dogs and cats can react to an ingredient in their food. This can also show up as extreme itchiness. In fact, a fair proportion of dogs’ ear infections are the result of food allergy, and a change of diet could ease the symptoms. For cats with food allergy, the classic sign is licking herself raw and scabby.

Indeed, Dr. Debora Lichtenberg, VMD, wrote a great article here on Petful about conducting a food trial to check if food is causing these skin breakouts, so I won’t dwell on that now. What I want to talk about are the pitfalls of hypoallergenic products and why they might not work.

Shampoo Sensitivity

Let’s say you have a dog with highly sensitive, itchy skin. It’s a good idea to bathe him regularly because this washes allergens off the skin’s surface and moisturizes it (with the right shampoo). However, his sensitive skin means that regular shampoos make his skin beaming red and intensifies the itch rather than relieves it.

Let’s take a closer look at that shampoo: You read the ingredients and discover it contains chemical cleaning agents including sulfates and parabens, synthetic fragrances, foaming agents and coloring. With that cocktail, it’s hardly surprising that you now have one itchy pet.

The next time you bathe the dog, you decide to use a hypoallergenic shampoo. You have high hopes, but a short time after the bath, it’s back to the familiar thump-thump-thump of your dog’s back leg in his armpit.

At this point, you’re probably scratching your head. Surely, hypoallergenic means “unlikely to cause allergic reactions,” so what’s really going on?

Hypoallergenic Shampoos

You read the label, and this product contains only natural ingredients. So far, so good.

The active ingredients are aloe vera, oatmeal, chamomile and rosemary, which all sound safe and healthy. The shampoo has hundreds of 5-star reviews from satisfied customers who have highly allergic dogs, so why is yours hot, red and itchy?

The answer lies in how hypoallergenic products work. They have 2 benefits:

• Purity: They contain fewer ingredients, and these are either natural or pure. This means fewer chemicals, which means kinder to skin.
• Restricted ingredients: Fewer ingredients means fewer potential allergens.

However, if these ingredients include something your dog is sensitive to, then his skin will react. Think of this as you would with a friend who has a seafood allergy: You could make her a sandwich using just 3 ingredients: bread, butter and prawns. As pure as the sandwich is, your friend’s going to swell up and need a trip to the ER.

This is because allergies work as a simple equation:

• Receptor + allergen = allergic reaction

In other words:

• Skin sensitive to rosemary + rosemary in shampoo = allergic reaction

It’s all in the details. What hypoallergenic actually means is these products are just less likely to trigger an allergic reaction. No product can be guaranteed not to provoke an allergy. It’s not the hypoallergenic shampoo’s fault — you were just unfortunate that this particular product contained something to which your pet is sensitive.

Skin Patch Tests

In an ideal world, your dog would have skin patch tests. You may be familiar with these from human medicine, where the clinician draws a checkerboard on your arm and pricks tiny amounts of allergens into the skin. The bigger the resulting bump, the more allergic you are.

This itchy dog just can’t get any relief after her bath:

Veterinary dermatologists do this test to give a definitive list of what your dog reacts to, which enables you to avoid those ingredients in products. This is great in theory, but traveling to see a veterinary dermatologist may not be practical. Also, the patch test uses common allergens but can’t test for every single substance, so it does have limitations.

A sensible alternative is to patch test a small amount of your chosen shampoo on a small area of your dog, such as on the shoulder or the rump (just as you would do with a new skin product or hair dye for humans).

By all means, use hypoallergenic products, but don’t be disappointed by their limitations.

This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Oct. 13, 2018.