If you know a little about mold, you may know that it has several parts.  (Check out our article here for more on the basics of mold).  There is the hyphae (what most people would liken to roots and stalks), that form colonies called mycelium, and then there are the spores (the seeds that get carried around in the air).   I was under the impression that mold spores were the only parts of mold that could revive after extreme dry conditions.  I was wrong!  There is a lot of research regarding survival of hyphae without spores (just the branches).   

A sclerotium is a compact mass of hardened fungal mycelium containing food reserves. One role of sclerotia is to survive environmental extremes. In some higher fungi such as ergot, sclerotia become detached and remain dormant until favorable growth conditions return...Sclerotia are rich in hyphae emergency supplies, especially oil. They contain a very small amount of water (5–10%) and can survive in a dry environment for several years without losing the ability to grow....In favorable conditions, sclerotia germinate to form fruiting bodies (basidiomycetes) or mycelium with conidia (in imperfect fungi). (Wikipedia)

Most sclerotium infect food crops and vegetation, but there is some evidence that it can be a problem for air quality.   They are classified as developing from white and gray molds.  According to this article, 

• A 2022 paper found a “strong positive correlation” between gray mold and the body’s creation of an inflammatory protein associated with asthma (interleukin-17A.)
• B. cinera is a gray mold that produces schlerotium.  It is less prevalent in indoor environments (about 1.1%), but a substantial proportion of patients were allergic to it (Exposure to the airborne mould Botrytis and its health effects)

It's hard to find survival duration estimates of mold spores, but it's estimated they can survive for years, even indefinitely.  This 2023 paper researched how spores that fully dry out are actually more viable than spores that were stored in more hydrated states.  The drying process actually stops depletion of energy reserves, so that the spore can go into a prolonged dormant state.  

Perhaps you’ve heard of “The mummy’s curse", or the premature deaths of explorers who entered King Tutankhamen’s tomb in 1922, and after the opening of a Polish king’s tomb in 1973.  These deaths were most likely due to inhalation of a virulent form of Aspergillus flavus (mold).  Indeed,  Dr. Sylvain Gandon is a French researcher who published research in 1998 showing that the longer spores survive, the more virulent they are when host infection occurs.  Considering that the Egyptian King Tutankhamen was entombed for approximately 3246 years and the Polish King Casimir IV was entombed for 481 years before the tombs were opened, these are incredibly long times for dormant mold spores to survive.  The wave of deaths following the exploration of the Polish King’s tomb was most likely due to the hasty manner in which the king’s body was prepared for burial, because he died during a hot period of the summer and started to decompose quickly.  After burial, the body and wooden coffin became a “biological bomb” of deadly fungus, which overcame 4 of the team within a few days of opening it, and a total of 15 people over several more years. (The Cursed Tomb of the Polish King Casimir IV Jagiellon)  More recently, a traveling exhibition of mummies in Mexico concerned health experts when fungus was spotted on one of the bodies. (Mummy exhibit with ‘fungal growths’ may pose health risks, experts fear)

This information can be applied to practical use in your own home.  If you have a water leak that starts to grow mold, "drying out" the environment is only the first step.  If the mold is not removed after, it can be primed to come back with a vengeance because the spores are fully dry.  You don’t want a smoldering “time capsule” of mold to come back and bite you or anyone else in the future, so it’s advisable to do what the experts do: not only kill the mold, but clean up the mold.  Make sure to only clean using masks and HEPA filters, and clean out the vacuum cleaners you use afterwards as well! 

Photo by Narciso Arellano on Unsplash