Summary of Key Points
The common red stains found at home (on toilet seats, shower curtains, water cups, pet bowls, etc.) are not caused by rust, but rather by two types of microorganisms: Serratia marcescens or Red Yeast. These organisms are widespread, thrive in humid environments, and can survive in places that contain almost only water. Their presence is unrelated to the quality of tap water; in fact, water filters or water that has been left standing for a long time may even promote their growth. They are generally harmless to healthy individuals, but people with weakened immune systems may be at risk of infection. To remove these stains, it is essential to combine cleaning with disinfection, and the most important step is to maintain a dry and well-ventilated environment.
1. Red Stains Are Not Rust! They’re Caused by Two Microorganisms
The red stains you see are usually not due to rust but are the result of the activity of two microorganisms:
- Serratia marcescens: A type of bacteria that produces a bright red pigment, giving its colonies a reddish appearance.
- Red Yeast: A type of fungus that also secretes a red pigment and often attaches to plastic surfaces (such as pet bowls).
The colonies formed by these microorganisms are very noticeable, which is why you easily spot them.
2. Why Are Humid Areas in the Home Always “Stained” Red?
These microorganisms can establish themselves in your home because they possess two “superpowers”:
- Widespread Distribution: They can be found in soil, water, and air, and can easily enter your home through the air.
- Drought Tolerance: They do not require abundant nutrients. They can survive in soap residue in sinks, small amounts of organic matter around toilets, or even in water that seems clear but actually contains some moisture. Their preferred environment is humid, and with just a little water and food, they can multiply.
3. Can Water Filters Make the Stains Worsen? Standing Water Can Also Contribute to Growth
Don’t assume that poor water quality is the only cause of red stains. In fact:
- It Has Nothing to Do with Water Quality: These microorganisms are not attracted to dirty water.
- Water Filters May Backfire: Water filters remove chlorine from the water, which serves as a natural barrier against their growth. Without this barrier, the microorganisms can multiply more quickly.
- Standing Water Is Particularly Problematic: In unused toilets, for example, the chlorine in the water gradually dissipates, allowing the microorganisms to become more active.
4. Are They Dangerous to Humans?
These microorganisms are not particularly harmful, but they should be taken seriously by certain groups:
- Healthy People Are Generally Fine: They have a low ability to cause illness, and most people with a normal immune system will not get sick from contact with them.
- Vulnerable Groups Need to Be Cautious: People who are hospitalized, have weakened immune systems, or are newborns may be at risk. These microorganisms can become opportunistic pathogens, potentially causing infections in the lungs, wounds, or urinary tract. Serratia marcescens can also lead to sepsis in severe cases, while Red Yeast can attach to plastic tubing, increasing the risk of hospital-acquired infections. Additionally, some strains of these microorganisms may be resistant to antibiotics, making treatment more challenging.
5. How to Remove Red Stains?
To get rid of these red stains, follow these steps:
- Clean the Surface: Use a regular cleaner to remove visible stains, but it is difficult to completely eradicate them since they can easily reappear.
- Disinfect and Prevent: Spray a solution containing chlorine (such as 84 Disinfectant) on areas where they tend to grow. Let it sit for 10–20 minutes before rinsing off to kill most of the microorganisms. It is also crucial to keep the environment dry and well-ventilated. Improve bathroom ventilation, ensure drainage is unobstructed, and regularly clean water cups and pet bowls to reduce their breeding grounds.
(Note: Although this is a scientific explanation, it has been presented in plain language to make it easy for non-experts to understand.)