Maxillofacial teams increasingly encounter patients who live, work, train, or deploy in extreme environments—arctic cold, hyperarid deserts with intense solar exposure, high-altitude hypobaric hypoxia, tropical humidity, and hyperbaric settings during diving or in therapeutic chambers. This chapter synthesizes maxillofacial-relevant evidence on how these environments perturb facial skin, oral mucosa, salivary function, sinonasal cavities, craniofacial neurovascular control, wound biology, and reconstructive outcomes. It focuses on clinical implications for prevention, diagnosis, perioperative care, and reconstruction, while strictly grounding statements and citations in the provided source extracts. In-text citations use the Harvard Name/Year style, and a complete reference list is appended.