It has been established for some time that moulds including Aspergillus love to grow on wallpaper especially if it gets a little damp, even if the damp is relatively short lived but repeats regularly. We also know that moulds such as Aspergillus can sometimes produce mycotoxins that are highly toxic when growing on building materials, though what is less sure is if this presents a reals hazard to inhabitants of a building containing damp & mouldy wallpaper.
As with all toxins the amount of toxin taken in is vitally important when predicting the outcome with respect to human health. For example the average amount of caffeine in our diets does not cause illness, merely acting as a stimulant to wake us up in the morning, however if we were to drink just fifty times more it would rapidly kill us!
It has yet to be demonstrated if enough mycotoxin can be generated in a damp home and come into contact with a person sufficiently to make us ill, despite several attempts to do so. However the possibility remains that a combination of several different kinds of toxin acting together over a long time might cause a chronic illness as yet not clearly defined. Chronic exposure to low levels of toxin is gaining more attention and concern in several fields of human health, so perhaps exposure to sub-acute levels of mycotoxin might yet be firmly linked to an illness.
As a good first step we need clarification of which fungal species are found on materials commonly found indoors and information on when we might see them produce mycotoxins. We also need evidence for how readily toxins produced by fungi growing on a wall for example might be released into the air, and firm evidence that the quantity of toxin produced could pose a threat to health.
Aleksic et.al (2017) have just published a research paper that shows that mycotoxins mycophenolic acid, sterigmatocystin and macrocyclic trichothecenes (made up of 4 major compounds) are produced by three fungi (including Aspergillus species) when grown on wallpaper. They have shown that mycotoxins can be produced in hundreds of mg/m2 of wallpaper and that the toxins can be partly made airborne in a steady draught of air or sudden gusts that are realistically attained under normal living conditions in a home or other building. This is valuable information for the process of assessing the risk to human health caused by mycotoxins and no doubt fungal allergens produced under these common circumstances.
The study cannot and does not attempt to extrapolate these results to speculate upon whether the levels of exposure they detect might cause a health problem if breathed in. The results show us how much mycotoxin and which mycotoxin might be produced on wallpaper in a damp home, and how much might be transferred into the air. Once in the air there is potential for some of that to be breathed in, but we need more guidence on how much might be breathed in by someone living in such a home in the average day, how much might accumulate in their bodies and whether or not toxic levels could be reached, acute or chronic.