Why does atopic dermatitis itch?

Neural and chemical mechanisms are involved. When the epidermis and its nerve fibers are stripped from skin, pruritus is abolished. Keratinocytes and mast cells release high levels of nerve growth factor (NGF), which increases the sensitivity of cutaneous pruritus receptors. These sensitized nerve endings demonstrate an increased capacity to transmit signals that are perceived as pruritus (allokinesis). Chemical mediators associated with itch include serine proteases, interleukins 2 and 31, opioids, acetylcholine, prostanoids, and substance P. Histamine may play a limited role in the pruritus of atopic dermatitis. These mediators act either on nerve endings or  directly on keratinocytes. They are produced by mast cells, keratinocytes, T cells, and nerve fibers.

Yosipovitch G, Papoiu ADP: What causes itch in atopic dermatitis? Curr Allergy Asthma Rep 8:306–311, 2008.