Primary hyperhidrosis is a pathologic condition that is characterized by excessive sweating beyond the physiological needs required for thermoregulation. It affects 0.6–5% of the world population and inflicts a significant impact on the quality of life in affected patients. The exact pathophysiology of primary hyperhidrosis remains unclear, but the prevailing theory of pathogenesis appears to be neurogenic hyper-excitability of the sympathetic nervous circuits innervating eccrine glands. In this paper, we aim to review the normal physiology of thermoregulation and discuss several theories and current evidence on the pathophysiological features of primary hyperhidrosis.