Radon-222 and its progeny are a Group 1 carcinogen (IARC), the second-leading cause of lung cancer. Delivered at a MEASURED dose — ~5.0 mSv to the lungs and ~4.4 mSv to the skin in the thermal-gallery pathway (PMC8535235) — with a latency (5–7 yr leukaemia, 10–60 yr solid tumours) long enough that the cancer risk of a given course cannot be attributed after the fact. This is the modality whose dose is written down, and it is a dose of a carcinogen. The risk leads the row.
A delivered modality on an ionizing carrier, with a real and contested literature — including controlled trials in rheumatic indications. Radon-222 and progeny are inhaled in a gallery/vapour cabinet or absorbed through the skin in a bath; the doses differ by route and are NOT interchangeable. The atlas's cleanest example of a written-down dose — of a Group 1 carcinogen.
Origin & lineage
Bad Gastein (Austria), Jáchymov (Czechia) and other radon galleries, mines and baths.
Claimed mechanism
Low-dose ionizing radiation (radon-222 + progeny) is claimed to produce an immunomodulatory / analgesic (hormetic) effect in rheumatic disease.
Plausibility
Contested, not physically impossible — low-dose radiation immunomodulation is a live scientific question; no contradicts badge.
Evidence — grade B/C
B/C (editorial — B defensible, recorded as a decision not a finding). FOR B: a meta-analysis of five RCTs (Falkenbach, PMID 14673618, Rheumatol Int 2005; 338 patients) plus randomised trials (Franke 2000, PMID 10952746, Rheumatology 39:894–902; IMuRa, DOI 10.1007/s00296-013-2819-8) support a pain benefit from a radon COURSE. AGAINST: RAD-ON02 (DOI 10.3389/fimmu.2023.1284609; companion 10.3389/fimmu.2024.1307769), designed to hold the thermal bath constant and vary only radon, found BOTH ARMS IMPROVED and radon's superiority appeared at ~4 weeks WITHOUT holding beyond short-term follow-up. TWO TIME SPANS, KEPT APART: ~40 weeks belongs to the COURSE (heat+humidity+radon+regime), ~4 weeks is how long radon's separation from plain warm water survived once the confound was broken — a row that reports only the 4 weeks reads as a refutation, which it is NOT. A 2026 review (DOI 10.1007/s10067-026-08202-y) says the isolated efficacy remains uncharacterised. Not Tested-not-confirmed: blinded testing partially SUPPORTED then failed to sustain separation.
A delivered, dosed intervention on an ionizing carrier with a real controlled literature — and a written-down dose, which almost nothing else in the atlas can claim. The classical gallery course is MULTI-MODAL (heat + humidity + radon at ~44 Bq/l); cross-reference the thermal family, do not merge.
Set aside — claim
The radon-specific benefit over plain warm water did not hold beyond ~4 weeks once isolated; the ~40-week persistence belongs to the whole course, not the radon. Gallery and bath are different routes at different doses and must not be averaged.
Regulatory status by jurisdiction
Registration or clearance is a market-access fact, never proof of efficacy.
US — FDA
No therapeutic radon indication.
EU — MDR
Radon cures are reimbursed in parts of Europe (Austria/Germany traditions).