Atopic dermatitis or atopic eczema is a skin rash that’s particularly common among young children, but can last into adulthood. “Atopic” refers to an allergy, “derm” refers to the skin, and “itis” refers to inflammation.
So atopic dermatitis describes skin inflammation that results from an allergy, more specifically, it happens when the immune system attacks the skin causing a dry, itchy rash on flexor surfaces of the body, areas like the creases of the wrists, the insides of the elbows, and the backs of the knees, as well as exposed skin surfaces like on the face, the hands, and the feet.
When the immune system inappropriately starts attacking itself, we call that a hypersensitivity reaction, and there are four types.
Atopic dermatitis is a type 1 hypersensitivity reaction, and it starts off with something in the environment called an allergen, like flower pollen.
The pollen is able to travel through the slightly porous skin, where it gets picked up by an immune cell in the tissue just below.
The immune cell is called an antigen presenting cell because it presents a bit of the allergen to a naive T helper cell, activating it into a Th2 cell.
This Th2 cell then stimulates a nearby B cell to start producing IgE or immunoglobulin E antibodies specific to that pollen.
Those IgE antibodies bind to the surface of other immune cells called mast cells, as well as basophils, which can be found in the tissue layer just below the surface of the skin, and this process called “sensitization”.