During an <a href="https://en.wikipedia.org/wiki/asthma" class="extiw" title="w:asthma">asthma</a> episode, inflamed <a href="https://en.wikipedia.org/wiki/bronchiole" class="extiw" title="w:bronchiole">airways</a> react to environmental triggers such as smoke, dust, or pollen. The airways narrow and produce excess <a href="https://en.wikipedia.org/wiki/mucus" class="extiw" title="w:mucus">mucus</a>, making it difficult to breathe.
FDA/Renée Gordon; vectors by <a href="https://en.wikipedia.org/wiki/User:Mysid" class="extiw" title="w:User:Mysid">Mysid</a>.
2008-09-20
Vectorized in Inkscape by <a href="https://en.wikipedia.org/wiki/User:Mysid" class="extiw" title="w:User:Mysid">Mysid</a> from <a rel="nofollow" class="external free" href="http://www.fda.gov/fdac/features/2003/203_asthma.html">http://www.fda.gov/fdac/features/2003/203_asthma.html</a>