The history of Fallout 76 collectibles has had almost as bumpy a road as the game itself, beginning with the whole canvas bag fiasco, continuing with a rather unattractive (and expensive) (and widely mocked) leather jacket, and culminating most recently with a T-51 power armor helmet that had to be recalled due to a mold risk.
The T-51 replica helmet, made by Chronicle and sold by Gamestop, contained a polyester/cotton blend fabric liner that posed a risk of mold exposure, which could potentially lead to a respiratory infection or other health issues.
If you weren't one of the lucky customers who bought a moldy T-51 power armor helmet for $150, at least you can experience it virtually. Naturally, a modder has added the moldy power armor helmet to Fallout 4.
The Moldy T-51 Helmet mod adds a helmet that, when worn, will give your character constant radiation damage. Flavor text states the polyester/cotton blend fabric liner resulted in a recall of the power armor helmets during the war due to the adverse effect on the wearer's health.
You'll need to own the Nuka-World DLC to put the moldy helmet on your character's head and start damaging their lungs. The moldy liner can be found under 'Misc Mods' in your power armor crafting menu. Enjoy.