Why does atopic dermatitis itch?

Abstract

　Itch has been defined as an unpleasant sensation that evokes the desire to scratch. Itch is also believed to signal danger from various environmental factors or physiological abnormalities. Itch sensation is induced via nerve endings in the skin whose cell bodies are located in the dorsal root ganglia (DRG) and trigeminal ganglia. Neuronal excitation propagates to the brain through the spinal cord dorsal horn, inducing an itch sensation. Therefore, it is believed that itch hypersensitivity and chronic itch may involve abnormalities in neurotransmission or neural circuitry from skin to brain. Antihistamine-resistance and intractable itch impair quality of life (QOL) , and frequently accompany inflammatory skin conditions and systemic diseases. In some cases, intense itch impairs QOL more so than pain. Such itch is present in patients with atopic dermatitis (AD) . As first-line antipruritic therapy, antihistamines (H₁-receptor antagonists) are commonly used in treatment of AD, although it is often difficult to control the itch. This review describes present knowledge regarding mechanisms of antihistamine-resistance and intractable itch.