The role of a recently discovered peptide—irisin—in physiological and pathological processes

Irisin, a cleaved fragment of fibronectin type III domain-containing protein 5 (FNDC5), was originally described as a factor stimulating browning of white adipose tissue, produced during physical exercise by skeletal muscles. However, irisin is not only a new and promising biomarker of metabolism; its expression has been found in a wide variety of tissues and organs such as the peripheral nerves, stomach, pancreas, and skin, and recent data also indicate its role in cancer. Numerous studies focus on the protective role of this protein, which could become an important factor in predicting disease risk, disease prognosis, or possible metastases in cancer patients. Possible use of irisin in therapy is also worth considering. The aim of this paper is to systematize knowledge on the role of irisin in patients and to draw attention to its role in skin diseases including acne vulgaris, psoriasis vulgaris, and hidradenitis suppurativa.