There is one condition that rules the therapy out completely, and a longer list of conditions that have to be weighed.
The absolute one is short. The only true absolute contraindication is untreated pneumothorax, a collapsed lung that has not been treated. Treating a patient in this situation would lead to rapid progression and would be fatal.
Everything else is relative, meaning weighed rather than forbidden. Most of these relate to barotrauma. That’s injury to a closed, air-filled space, such as the lung or middle ear, when trapped gases expand as the pressure changes.
The relative contraindications are pulmonary blebs, and emphysema with carbon dioxide retention; sinusitis; seizures; pregnancy; implanted devices such as pacemakers; and epidural pumps. Claustrophobia can also be an issue, especially in a monoplace chamber.
Certain medicines are on the list too, each for its own reason. Disulfiram blocks an enzyme that protects against oxygen toxicity. Cisplatin and mafenide acetate impair wound healing. Bleomycin can cause a lung complication.
Two things follow from this if you’re being considered for the therapy. First, make sure the unit has your full medication list, including anything prescribed elsewhere. Second, claustrophobia is a real clinical consideration, not something to be embarrassed about. It’s worth saying before a course rather than during the first session.
Nothing here is a way to decide whether the therapy is safe for you. That assessment is made by the unit. This page is here so you know which things are worth mentioning.