5 Common Mold Myths, Debunked

Most of what homeowners believe about mold is half-right, and the half that is wrong is usually the expensive half. Below are the five misconceptions that come up most often on San Diego jobs, with what is actually true in each case.

Myth 1: Mold is always harmful and serves no purpose

Reality: Mold is a natural and necessary part of the outdoor environment. It breaks down dead organic matter, and specific species are used deliberately — Penicillium in antibiotics, Aspergillus oryzae in soy sauce and miso, Penicillium roqueforti in blue cheese.

The problem is not mold as an organism. The problem is amplified indoor growth — a colony feeding on your drywall, releasing spores into air you breathe eight hours a night. Outdoors it belongs. Indoors, growing on building materials, it does not.

Myth 2: If it has not made me sick yet, it will not

Reality: Reaction to mold varies enormously between people and within the same person over time. The Centers for Disease Control and Prevention notes that people with asthma, allergies or weakened immune systems can have more severe reactions, and that damp indoor environments are associated with respiratory symptoms including coughing, wheezing and congestion. (Source: CDC — About Mold and Your Health)

Two things follow. First, a household member who is fine today can react badly after a course of immunosuppressants, a pregnancy or a chest infection. Second, “nobody feels sick” is not evidence that the growth is harmless — it is evidence about the current occupants, on the current day.

Myth 3: A healthy home should have zero mold

Reality: Mold spores are present in essentially all indoor air, everywhere, all the time. They come in through open doors, on clothing, on pets. No remediation removes them permanently and any company promising a “mold-free” home is describing something that does not exist.

The realistic goal is different: remove active growth, return indoor spore levels to something comparable with outdoor levels, and eliminate the moisture that let the colony establish. That last part is what actually prevents recurrence. Mold that returns to the same wall three times is a plumbing or ventilation problem being treated as a cleaning problem.

Myth 4: If you cannot see it, you do not have it

Reality: Individual spores are microscopic. What you see as a black or green patch is a colony that has already grown to millions of organisms. By the time it is visible on a wall surface, there is very often more of it inside the cavity behind that wall.

Hidden growth is common in these places:

• Inside wall cavities, fed by a slab leak or a pinhole in a supply line.
• Under vinyl or laminate flooring, where moisture is trapped rather than evaporating.
• Behind bath and kitchen cabinets.
• Above ceiling tiles and inside soffits.
• In AC ductwork and around the air handler — see mold in your AC ducts.
• In crawl spaces and under subfloors.

A persistent musty smell with no visible growth is a genuine signal, not imagination. That odour is a by-product of active colonies metabolising, and it usually means growth somewhere you cannot see.

Myth 5: Bleach kills mold

Reality: This is the most costly of the five, because it feels like it works. Household bleach is roughly 94% water. Sprayed onto a porous surface such as drywall, wood or grout, the chlorine reacts at the surface and the water soaks in — carrying the structure below the surface and feeding what is left of it.

What you get is a lightened stain and a colony that returns, often larger, in a few weeks. On non-porous surfaces such as glass, sealed tile or stainless steel, bleach is a reasonable surface cleaner. On porous building materials, contaminated material generally has to be cut out and disposed of, not treated in place.

What is actually true: the numbers worth remembering

• Mold can begin growing on damp material in 24 to 48 hours. This is the single most useful figure in the category.
• The EPA advises that growth covering more than roughly 10 square feet should be handled professionally rather than by the occupant. (Source: EPA — Mold Cleanup in Your Home)
• Indoor relative humidity should sit between 30% and 50%. Above 60% sustained, mold can grow with no leak at all.
• Most indoor species grow between 68°F and 86°F — ordinary room temperature.

When a professional is the right call

Call someone in if the affected area is larger than about 10 square feet, if the water involved was sewage or ground flooding, if the growth is inside a cavity or duct where you cannot judge its extent, or if anyone in the household has asthma or a compromised immune system. Proper remediation means containment and negative air pressure so that removal does not distribute spores through the rest of the house — which is exactly what unprotected DIY demolition does.

Get an inspection rather than a guess

Smart Dry Restoration inspects, tests and remediates mold across San Diego County to IICRC guidelines, and documents moisture readings for insurance purposes. If you have visible growth, a musty smell you cannot locate, or a leak you have just found, call (858) 433-5100. Dispatch runs 24 hours a day.

Related reading: mold remediation in San Diego · what causes mold to grow