While this is a simple question, the answer can be complex. To keep it short and sweet: most forms of mold are benign, if not exactly healthy to have in your home, but a small number of mold species are toxic. Identifying those types of molds that are actively dangerous can be difficult, however, because mold and fungal growths come in thousands of species. The fungal growths that occur as a result of wood rot, for example, can look similar to white forms of mold but are generally not harmful to humans unless ingested (though they will wreak havoc on your home). The type of mold that you should be most worried about, however, is black mold. Black mold is highly toxic to humans and animals; it can cause serious side effects even when the level of exposure is small. Black mold can cause side effects such as rashes, skin irritation, infections, dizziness, breathlessness, respiratory issues, and, in some very serious cases, seizures. More serious side effects are rare, of course, and tend to only occur after prolonged exposure… unless there are underlying issues. As is so often the case, those who are already vulnerable are at the most risk from exposure to any kind of mold but particularly when exposed to black mold in any serious or prolonged capacity. Those most at risk are the elderly, very young children, those who have underlying respiratory issues such as asthma, bronchitis, or emphysema, and those who have impaired immune systems. While exposure to black mold can be unpleasant and debilitating for anyone in large doses, even a small amount of exposure can be lethal to people who have underlying conditions. That makes it necessary to seek out waterproofing measures that can protect your home from falling victim to this kind of infestation.