Hydrogen applications face sealing challenges. Often, these seals are made of PTFE and work under fretting conditions. Experiments in this study were conducted with PTFE against 52100 steel under varying humidity. Results show significant wear of PTFE in hydrogen, regardless of humidity, with PTFE transferring onto steel surfaces. FTIR and XPS analyses reveal that hydrogen's reducing effect suppresses surface metal oxide formation, inhibiting tribochemical reactions. However, when hydrogen is diluted with nitrogen, PTFE's tribological performance improves, though tribochemistry is not promoted. Only with oxygen and water vapour do tribochemical reactions occur in H2, where metal fluoride is first formed, followed by carboxylate chelates. These findings highlight the critical role of hydrogen's reducing nature, offering insights for developing advanced sealing materials.