Last year, we found out that astronauts circulating about 240 miles above the Earth in the International Space Station (ISS) have to scrub down the interior of their ship to remove black mold that is in the walls.

Scientists now know spores of the two most common types of mold on the ISS — Aspergillus and Penicillium — can survive X-ray exposure at 200 times the dose that would kill a person.

Fortunately, molds are not particularly harmful unless you have an allergy or hypersensitivity to them. That can trigger asthma and hay fever-type symptoms such as sneezing, runny nose, red eyes, and skin rash.

One study in the journal Clinical Reviews in Allergy & Immunology says the "symptoms of memory loss, inability to focus, fatigue, and headaches ... were reported by people who erroneously believed that they were suffering from 'mycotoxicosis.' Similarly, a causal relationship between cases of infant pulmonary hemorrhage and exposure to 'black mold' has never been proven. Finally, there is no evidence of a link between autoimmune disease and mold exposure."

Still, you do not want mold in the house, damaging walls, tile grout, or your health.

To prevent mold from appearing, use a dehumidifier in damp areas, repair leaks and drips immediately, and prevent moisture from pooling outside your home.

If you have to remove moldy, porous materials on walls or ceilings, check out the Environmental Protection Agency's "Mold Remediation in Schools and Commercial Buildings" at epa.gov. It's got great information anyone can use.