Focal hyperhidrosis is caused by sympathetic hyperactivity and can be further divided into primary or secondary form according to its etiology. Primary focal hyperhidrosis usually has an onset during childhood or adolescence and lasts throughout the life of the patient. It can be exacerbated by environmental and emotional factors and usually affects the palms, soles, axillae and occasionally, craniofacial region. In contrast, secondary focal hyperhidrosis is caused by systemic diseases or medications and usually has generalized effects and onset in adulthood. Though there has not been any record of severe mishap resulted from hyperhidrosis in our military history until now, flight surgeons should be aware of the influences of the comorbidities of mild to moderate hyperhidrosis and the complications relating to the treatment of the disease in order to secure flight safety.