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Background: Hypohidrosis can result in heat injury, a potentially fatal condition. The majority of hypohidrosis cases have no associated abnormalities or secondary causes, and are termed “isolated hypohidrosis”. These are clinically divided into miliaria profunda (MP), acquired idiopathic generalized anhidrosis (AIGA) and idiopathic partial hypohidrosis (IPH). The pathogenesis of isolated hypohidrosis remains largely unknown and there is no established effective treatment. Objectives: To elucidate the pathogenesis of isolated hypohidrosis using in vivo high-definition optical coherence tomography (HD-OCT) imaging and assess the therapeutic profile of oral retinoids for this condition. Materials & Methods: We conducted a retrospective analysis on all patients with isolated hypohidrosis in our neuro-dermatology clinic over a 5.75-year period. All patients routinely underwent standardised exercising and whole-body starch-iodine testing, followed by non-invasive HD-OCT skin imaging. Patients’ demographics, disease characteristics, histology and treatment history were analysed. Results: Of the 51 patients identified with isolated hypohidrosis; 23 were diagnosed with MP, 14 with AIGA, and 14 with IPH. In these patients, HD-OCT imaging led to the identification of sub-stratum corneal hypo-refractile material with underlying dilated sweat ducts, not present in healthy controls. The size of this material was most pronounced in MP, followed by AIGA, and then IPH. Post-treatment, the material decreased in size. Treatment response was reported in 90.6% patients with isotretinoin and 75.0% with acitretin. No recurrence has been reported to date. Side effects were largely anticipated and common. Conclusion: The pathogenesis of isolated hypohidrosis involves obstruction of sweat orifices at the stratum corneum. Treatment with oral retinoids, particularly isotretinoin, is effective and safe.