What is Atopic Dermatitis?

Let’s take a look at what atopic dermatitis is, and how it happens. It really helps to understand what the skin is supposed to do, as this helps us understand the implications when it goes wrong.

The Skin Barrier: Our Dog’s Natural Defence System

Your dog’s skin is a protective layer, designed to keep foreign things out and moisture in. Let’s break down its key elements:

The Epidermis: This outer layer acts as a sturdy wall, composed of tightly packed cells called keratinocytes. These cells constantly renew themselves, with new cells forming in the deepest layers of the epidermis and moving outwards as they age. This forms a continuous barrier against harmful invaders like bacteria, viruses, and allergens. There are several layers in the epidermis, which aren’t important to know but are illustrated below if you’re interested.

The Dermis: This deeper layer serves as the fortress’ foundation, housing vital structures like blood vessels, nerve endings, hair follicles, and oil glands. These elements keep the skin nourished, hydrated, and supple.

Click or tap on the hotspots to read more about the skin structure

The Itch Alarm: How Do Dogs Feel and Respond to Itch?

Now, picture an allergen bypassing the fortress’ defences. This triggers a complex response within the skin, akin to an alarm system activating. Nerve cells detect the threat and send signals to the spinal cord and brain, essentially sounding the itch alarm.

Next, chemical messengers called cytokines join the battle, recruiting immune cells to neutralize the invader. These cells, in turn, release histamine, a powerful molecule that dilates blood vessels and activates other itch pathways. The result? An overwhelming urge to scratch!

The Itch-Scratch Cycle: A Vicious Loop That Needs Breaking

While scratching may offer temporary relief, it can create a detrimental cycle in the long run. It damages the skin barrier, making it even more vulnerable to allergens and irritants. This fuels the itch alarm, leading to more scratching, creating a vicious loop that can be challenging to break.

Atopic Dermatitis: When the skin barrier fails and the system overreacts

Dogs with atopy don’t have a good skin barrier, and it lets more through than it should. The first few times an allergen gets through, the dog’s immune system will treat it normally. But over time, the immune system becomes overly sensitive to the allergen, and the alarm system malfunctions. This “overreaction” leads to an exaggerated itch response, even to minor stimuli like grass pollen.

Atopy explanation video

The video below shows Dr Woodnutt, the vet who wrote this course, explaining the skin barrier and the reaction to allergens in dogs with atopic dermatitis.


The skin is designed to keep water in and everything else out. But in dogs with atopy, the skin barrier doesn’t function as well. It lets in allergens, and the dogs develop an excessive immune response to these allergens. They feel the need to itch at the most minor stimuli, and when they scratch they damage the skin barrier further, causing a vicious cycle of itching.

Key Takeaways

Atopic dermatitis is caused by a faulty skin barrier and an overactive immune system.