While not all people will experience obvious side-effects or negative health effects from the presence of mould in their home, exposure can cause allergic reactions, respiratory irritation and serious health concerns such as aspergillosis. Breathing in mould spores is particularly harmful for those with a compromised immune system or pre-existing medical condition such as asthma, as well as for the elderly and infants under 3. In serious circumstances, exposure to mould can lead to significant medical events or even hospitalisation.