CPAP, or continuous positive airway pressure, is a commonly used treatment for sleep apnea. However, there are certain situations in which CPAP should not be used. These include patients with severe lung disease, people with central sleep apnea, and those who cannot tolerate the machine. Additionally, CPAP should be avoided in patients with severe nasal congestion or sinus infections, as it may worsen these conditions. Other potential contraindications for CPAP use include patients with certain eye infections or recent eye surgery, as well as individuals with certain facial deformities.