Hyperbaric oxygen therapy (HBOT) involves breathing 100% oxygen at pressures above 1 atmosphere, typically 1.5–2.5 atmospheres absolute. The medical applications are well-established for specific indications including carbon monoxide poisoning, decompression sickness, and chronic non-healing wounds. The hair loss application is based on the theoretical mechanism of improved scalp tissue oxygenation potentially benefiting follicle metabolism.

The clinical evidence remains preliminary. A 2019 small Korean study of 20 patients with androgenetic alopecia receiving HBOT three times weekly for 8 weeks reported modest hair count improvements but lacked a control group. A 2022 case series suggested possible benefit when combined with minoxidil but couldn't isolate HBOT's independent contribution. No adequately powered randomised trial has been published.

The cost-benefit analysis is unfavorable. HBOT sessions typically cost £80–200 each, with protocols requiring 20–40 sessions for any potential benefit. Total costs of £1,500–8,000 are common, with no guarantee of result. For patients exploring all options after exhausting first-line treatments, the choice is defensible. For patients seeking cost-effective hair loss management, HBOT is not supported as a primary intervention.