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Facts About Mold: The Black Stuff in Your Toilet, Shower, or Sink



The grayish-black buildup that is observed in toilet bowls, and sometimes in shower stalls and sinks, is the result of fungal growth, more commonly referred to as black mold. In many cases this mold growth is composed of several different fungi and other organisms. The source of the fungi is microscopic airborne fungal spores that can be dispersed throughout the house by air currents.


Mold is a fungus that grows where there’s moisture. A good temperature (the same temperature range people prefer) and a food source are helpful, but the moisture is the real problem. All homes have spores floating around in the air, but homes with excess humidity are more likely to develop a fungal problem.

The fungus grows best in areas that are dark, warm and moist. Mold releases spores that continue to grow and multiply. The mold may appear black, green or even orange in color and form a ring in the toilet bowl. When you notice mold, remove it as soon as possible to prevent it from spreading. The mold may take over the toilet bowl and make it look dirty if you do not take the time to clean it properly.



There are many possible reasons for the appearance of mold in your toilet tank or bowl. If you’ve been gone for awhile, the stagnant water can breed the mildew, particularly if human waste has sat along with it, after only three days. Think about your bathroom. The toilet, the sink, the shower: all of those produce moisture, so having a mildew problem is very common. The very presence of your water is likely to attract spores. The water in the toilet is open to the environment and rapidly loses its chlorine residual. The internal area up under the lip of the toilet provides a refuge for the fungus. It is from here that the bowl is re-inoculated after cleaning. In most cases, growth reappears within several days after cleaning.


Routine cleaning provides only short-term relief.The bowl and the tank must be disinfected after cleaning.Adding bleach to the tank and bowl can do this.A contact time of 30 minutes or more must be allowed, then flush completely.This procedure might have to be repeated several times.It is important that all areas with fungal growth be treated at the same time to eliminate cross contamination.Be mindful that a strong solution of bleach, if left in the tank too long, can be corrosive to the metal and rubber components in your toilet. There are different products available for purchase that are designed to sit in the tank that provides disinfection with every flush.

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