We present the case of a 37-year-old woman who presented to the emergency department with dyspnea and was suspected of having summer-type hypersensitivity pneumonitis based on her medical history, imaging findings, and the presence of anti-Trichosporon asahii antibodies. Subsequently, her mother developed similar symptoms. An environmental provocation test was performed on the daughter and reproduced her symptoms within 12 hours of exposure to the suspected environmental trigger. An environmental investigation detected Trichosporon sp. in multiple locations where the daughter and mother frequently spent time, but not in the area where the father spent time. The daughter’s symptoms were alleviated through a combination of antigen avoidance and steroid therapy, whereas the mother’s symptoms were alleviated through antigen avoidance alone. Both patients remained asymptomatic after moving to a new residence. Our report demonstrates the diagnostic and investigative utility of environmental provocation testing and environmental investigation in identifying the cause of familial differences in the onset of summer-type hypersensitivity pneumonitis. Additionally, it emphasizes the importance of considering hypersensitivity pneumonitis as a possible diagnosis in cases of familial respiratory symptoms.