How does epidermal pathology interact with mental state?

The hypothesis is presented that human emotional state is influenced by epidermal pathology via the release from epidermal keratinocytes of a wide variety of chemical mediators (including neurotransmitters) that act on the brain. It has long been recognized that epidermal keratinocytes play a key role in the function of the stratum corneum as an impermeable barrier, and that skin diseases such as atopic dermatitis and psoriasis, which cause itching, sleep disturbance and concern over appearance, are associated with depression and anxiety. On the other hand, epidermal keratinocytes are known to produce and release multiple cytokines and chemical mediators in response to barrier impairment or insult, such as environmental dryness or UV radiation. Elevation of plasma cytokines is associated with depression in cancer patients. Serum levels of oxytocin and glucocorticoid have been shown to influence mental state, and a recent study showed that glucocorticoid is generated in injured epidermis. Thus, there are multiple plausible pathways through which changes in skin can affect emotional state.