Does Usnea (Old Mans Beard) have negative effects on the respiratory system?
According to the Institute for Traditional Medicine and the Gale Encyclopedia of Alternative Medicine:


Usnea (aka Songluo or "Old Man's Beard") is a fruiticose lichen (not a fungus).
Used in traditional medicine worldwide, including historically in China, Europe and by native Americans, as well as globally today. 


"Uses": topical antiseptic; therapuetic agent; medicinal herb; anti-cancer
It has traditionally been used in the treatment of bronchitis, in the treatment of tuberculosis, to ease coughing, to cleanse lungs and as an expectorant (i.e, to resolve phlegm). 


Contains a secondary metabolite, usnic acid, which is claimed to be an effective inhibitor of gram positive bacteria-including tuberculosis, staphylococcus, streptococcus, and pneumococcus




So Usnea is often used for the lungs. In fact, today, supporters of traditional medicine still use it rather regularly as an expectorant. I could find no sources that claimed that this was unsafe or had any negative effects on the respiratory system. I would think that if you were to inhale any usnea, its effects would simply rid your body of any particulates during expectoration.


However, a number of sources (e.g., see Sanchez
et al., 2006, here , here and here) mention that usneic acid can cause liver damage (and failure).  


Disclaimer: I did not find any reputable source acknowledging usnea to be effective at treating any of the aforementioned ailments. Use at your own risk. 



Citations


Sanchez, W.T., Maple, T.J., Burgart, L.J. &amp; Kamath, P.S. (2006). Usnic acidhepatotoxicity. Mayo Clinic Proceedings 81: 541-544