Mushrooms that sprout up in your bathroom are a cause for concern. Even though many mushrooms are harmless on their own, the presence of mushrooms indoors is indicative of a significant moisture problem that may lead to more serious mold infestations.
The fungal spores that generate mushrooms are microscopic and light enough to be carried by even small gusts of wind. Spores are present on clothing, window screens and plants, but two of the single-cell spores must combine to begin mushroom growth. Because mushrooms require high humidity and low light, the conditions inside your home generally don't support mushroom growth. Bathrooms, however, are particularly well-suited for sprouting mushrooms. High heat, excess moisture and low lighting provide the growing conditions that allow mushrooms to flourish on bathroom floors, walls or even ceilings, particularly around areas where moisture collects or pools.
Though the threat of poisonous mushrooms may be the first danger you consider, the mushrooms themselves are unlikely to pose a serious threat to your health. A majority of mushrooms are harmless, though you should not eat any mushrooms that grow in your bathroom as a matter of caution. The real danger of bathroom mushrooms is that they are a sign of a significant moisture problem that could support the more harmful growth of black mold or mildew. Mold and mildew flourish in the same conditions that support mushroom growth, and exposure to them poses a risk of serious allergic reactions or respiratory illnesses.
The initial removal of large mushrooms is as simple as donning a pair of rubber gloves and picking the offending fungi out of the floor, wall or ceiling. Once you remove the mushrooms, clean the area with a solution of 1 part bleach to 3 parts water. If mushrooms return, clean the area with a household disinfectant containing benzalkonium chloride to kill off any remaining mushroom spores, and apply a fungicide if necessary. Full eradication may require several applications of either a fungicide or a bleach solution.
Treating existing mushrooms in your bathroom with a fungicide is not enough to prevent future fungal problems there. If the levels of humidity in your bathroom are high enough to support mushrooms, they are also high enough to support the growth of toxic mold or structural damage to underlying wood structures in the room. Ensure that your bathroom is fitted with a ventilation fan to remove humidity. Wet towels also provide a breeding ground for mold and mushrooms, so hang towels to dry or transfer them immediately to a washing machine. If the seals around your toilet or bathtub are leaking or pooling water, have them repaired by a professional plumber. If your water damage problem is severe, you may need to replace flooring or walls with new, dry wood.