Mold isn’t always caused by a broken pipe, or leaky roof, or even a poorly vented bathroom. Sometimes the cause is human error and the lack of knowledge in understanding the conditions of your living space.
Hot spots are areas on exterior walls (usually where there isn’t great insulation) where the wall is at a low enough temperature to allow for condensation. This most commonly occurs when large pieces of furniture are left up against exterior walls. Mostly beds and couches, but dressers, desks and bookshelves can also produce this effect. And as it is out of the question to assume you can leave all exterior facing walls in your house free of furniture. Just being aware that this can cause mold growth on your interior walls isn’t common knowledge. The best thing to do in this and any situation is lower the relative humidity, you can do this by running the fan when showering or using a dehumidifier.If you are experiencing this make sure to pull your furniture away from the walls and make sure it can breathe behind it.
Below is an example of a bed pressed up against a poorly insulated exterior wall.