1. Your bathroom
Some of the more common germs found in a household bathroom are gastrointestinal viruses (stomach ailments), enteric pathogens (like E. coli bacteria), skin and respiratory organisms (like the staph infection), dermatophitic fungi (the most popular being athlete’s foot), and other residual fungi (think shower mold and mildew). Often, these potentially harmful organisms develop due to a lack of bathroom upkeep, but there are other, less obvious habits that can allow them to grow and spread.
Something as simple as not lowering the toilet lid when you flush can be detrimental, causing germy water to spray across the room and scatter bacteria onto surfaces that can settle into a lingering film. Other sources of bathroom moisture, such as wet towels and shower steam, can cause growth of bacteria and mold on multiple surfaces, like makeup brushes, loofah sponges, and toothbrushes. Your best bet is to wash your towels after every three or so uses, routinely replace your brushes and sponges, and be sure to run your bathroom fan to displace shower moisture.
To clean your bathroom, you should use a bleach-based solution on all surfaces on a weekly basis. And don't forget to clean your cleaning tools, too! Just because they're used to help you clean, doesn't mean they are clean. Clean your toilet brushes, plungers, scrubbing brushes, squeegees, and all other cleaning supplies, including water buckets.
It’s easy to become paranoid after hearing how strong and prevalent germs are in our world, but there’s no reason to become hysterical and go overboard. Keeping your home clean is a good practice to maintain, but you don’t want to be obsessive with it.