Carboxytherapy involves controlled subcutaneous injection of medical-grade CO2 gas using fine needles. The technique has been used in cosmetic dermatology for cellulite, dark circles, and stretch marks. The hair loss application is based on the theoretical mechanism: localised CO2 administration induces transient tissue hypoxia, triggering a compensatory vasodilation and improved local microcirculation, with potential downstream effects on follicle metabolism.

The clinical evidence remains preliminary. A 2019 Egyptian study of 50 patients with androgenetic alopecia compared carboxytherapy to topical minoxidil over 4 months. Both groups showed improvement; minoxidil produced larger effect (mean 14 vs 8 additional hairs/cm²). A 2022 study combined carboxytherapy with PRP and reported additive benefit, though the design didn't isolate carboxytherapy's independent contribution. Larger trials with rigorous controls are absent from the literature.

The honest assessment: carboxytherapy probably produces a modest hair-related effect through improved microcirculation, but the evidence is too thin to recommend it as a primary treatment. Costs are non-trivial (typically £80–200 per session, with protocols of 6–12 sessions). For patients seeking maximum evidence-based regrowth, the money is better spent on established treatments. For patients exploring multimodal approaches who have already exhausted first-line options, it's a defensible adjunct with limited but real biological rationale.