Of course, not all molds are toxic, and not all molds are black.  One of the most common molds found is Penicillium.   Penicillium chyrsogenum produces the antibiotic, penicillin, which could save your life.  But there are many other molds which can make you sick.  

Some molds, such as the infamous Stachybotrys chartarum, a.k.a. black mold, produce mycotoxins which, if inhaled or ingested, cause a number of symptoms ranging from chronic fatigue to headaches and vomiting.   Other molds, that do not produce mycotoxins, can produce allergens which cause hay fever-like symptoms and exacerbate asthma attacks.  With either the mycotoxin- or the allergen-producing molds there is an increased risk of infection to people who have suppressed immune systems.

In addition to the health problems they cause, molds can damage your property.  They actually consume the materials they grow on.  They can rot your wood, eat your drywall, and if left unchecked for long enough, they can cause structural damage to your home.  It is generally agreed that most molds are a nasty business, and it’s best to take measures to prevent them from gaining a foothold.

What can you do to help prevent mold from getting out of control in your home?

You can’t eliminate the spores altogether.   They can be tracked in on your shoes and clothing. They will hitchhike in on your pets.   When cool April breezes waft in through your open windows, they‘ll come along for the ride.    

Since you can’t eliminate the spores, you must keep them from growing.  To do this, you must keep in mind what they need to grow. 

In order to grow, mold requires moisture and nutrients.  Unfortunately for homeowners, mold’s idea of a happy meal might be the grout in your shower tiles, or the sheathing underneath your roof shingles, or the insulation between your walls.  Most building materials contain organic compounds, and it is organic compounds which feed mold.

Since it wouldn’t be practical or even possible to eliminate all the organic compounds in your home, you must, as much as possible, eliminate the moisture which is the other requirement of mold.   

Mold requires moisture to grow, but it doesn’t need a lot.  Relative humidity in the air over 60% is sufficient.    If the air in your home is too humid (it can be measured with an inexpensive device called a hygrometer) that can be enough to get a mold colony started.

The Minnesota Blue Flame Gas Association suggests these measures to decrease indoor humidity.

• Turn down or stop using humidifier.
• Use range and bathroom exhaust fans while cooking and bathing or open a window for a few minutes to bring in cool, drier air.
• Cook with pans covered.
• Take shorter showers with cooler water.
• Install a fresh air intake duct. Outside air introduced into the home lowers the humidity level.
• Reduce the number of plants in your home or water them less; they release water vapor into the environment.
• Vent clothes dryer to the outside.
• In tightly insulated homes, consider installing an air-to-air heat exchanger.
• In summer, use a dehumidifier.

From :  http://www.blueflame.org/datasheets/humidity.html#steps

Besides excessive humidity, there are other ways that moisture can get into your house, and promote mold growth. 

It may not be possible to keep unwanted water out of your home at all times.  Pipes burst, sinks overflow, floodwater gets in.  When unexpected occurrences douse your home, it is important to get the water cleaned up as soon as possible and the wet surfaces dried out.  Mold can begin to grow within 24-48 hours.

You can greatly reduce the possibility that water will invade your home and foster the growth of mold, by keeping your home maintained and in good repair.

Wood decks and exposed wood, such as around window sills should be painted or sealed.  Decks should be swept free from dirt and vegetation. 

You should repair obvious damage to your home as it occurs, and you should also inspect periodically for damage you might otherwise miss.  It’s a good idea to walk around and look at the exterior walls after heavy storms, and you should do a general inspection at least annually.

Inspect the roof by climbing into the attic after a heavy rain.   Bring a flashlight with you and look for wet or damp areas.  If the roof’s sheathing is wet or damp, it’s possible shingles have been damaged or blown off.  Missing or damaged shingles should be replaced as soon as possible.  If left unchecked, the wood underneath the shingles can deteriorate.

You should inspect painted wood siding for wear and peeling three years after it was last painted, and every year thereafter until it is painted again.  Wood soffit, fascia, and rake also need to be inspected and need to be repainted when the paint begins to show signs of wear.

Brick homes should be examined for damaged bricks or crumbling mortar. Crumbling mortar is a sign that the mortar is failing and should be repaired or sealed. Damaged bricks should be replaced.

Vinyl siding should be inspected for damage caused by hail or fallen tree limbs.  Any damage should be repaired before rainwater has a chance to penetrate the walls.   If the wood or insulation underneath the damaged siding gets wet, it can become a breeding place for mold and insects.  If the exterior of your house is covered with more than one covering material, such as brick and siding, the joints where the materials meet should be inspected for gaps.

You should inspect around windows and doors to make sure that caulking has not separated or pulled away because rainwater can get through the cracks. Leaks in basements should be stopped.

Plumbing fixtures, pipe joints, shut off valves, should be inspected for leaks.  Make sure there is no water or dampness in the cabinet underneath your sink . If your basement has a sump pump, it may be a good idea to install a battery backup so it will work during power failures.

Taking these preventive measures should greatly increase the likelihood that your home will need expensive repairs because of water damage and mold infestation.

What if you have mold already?

If you have seen visible mold or your home has a damp, musty odor, you should take whatever steps you need to get rid of it.   People around mold who do not show any symptoms, may develop symptoms with increased exposure.   People who show symptoms will find that their symptoms become more severe.

It is possible to remove small amounts of mold yourself but large or recurring areas may need professional remediation.  Ceiling tiles, drywall, insulation, carpet or other flooring that is moldy will need to be replaced.