To the asbestos, radon, lead paint and other household environmental hazards that give real estate agents headaches, add one more:

Toxic mold.

Concern about the potential health risks of certain kinds of mold has resulted in a number of highly publicized incidents and court cases in the past two years, especially in California and Texas.

The Delaware Supreme Court upheld a $1.04 million award on May 7 to two women whose landlord failed to address leaks and mold problems in their apartments, resulting in asthma attacks and other health problems.

Mold thrives most often in moist conditions. Moisture combined with a nutrient source such as soil, dust and products containing cellulose or other dead organic matter provides the ideal environment for colonization.

Though indoor mold always has been a problem, it has been aggravated by changes in construction techniques brought on by the energy crisis of the 1970s. Efforts to create energy-efficient houses without accompanying efforts to regularly exchange the air inside have been linked by the American Lung Association to a dramatic increase in cases of asthma in the past three decades.

"There is a heightened sensitivity to all environmental issues because of heightened air-quality concerns," said Paul Watson, an executive with ATC Associates Inc. of Downers Grove, Ill., a nationwide environmental consulting and engineering firm.

Not every mold is a potential hazard, Watson said. Without mold, for example, all cheese would taste the same, and penicillin would not exist.

Still, some segments of the population, such as asthmatics, are more sensitive to certain kinds of mold, especially when it is airborne.

The chief concern of late has been with Stachybotrys chartarum, or "black mold." While less common than other molds, this one is more dangerous to humans because it can, given the proper environmental conditions, create multiple toxic chemicals called mycotoxins.

These toxic byproducts exist in the spores of the mold, as well as in the tiny fragments that can become airborne. Of particular concern is the threat that humans will inhale and ingest these toxic spores.

According to the Centers for Disease Control and Prevention, there are few case reports that toxic molds inside homes can cause unique or rare health conditions such as pulmonary hemorrhage or memory loss. A causal link between the presence of a toxic mold and these conditions has not been proved, the CDC says.

But its argument holds little sway with Chris Clinton, who settled his family into their house in Chalfont, Pa., after moving from Florida more than two years ago.

After living in the house for a while, Clinton said, he started misplacing things. His wife began hyperventilating at night. His 9-month-old son developed upper-respiratory infections. His 3-year-old son had watery eyes, a runny nose and coughed frequently.

The culprit, Clinton said, was mold. The source: moisture from water leaks.

Clinton is spending more than $100,000 to rid the house of mold before he and his family move back in. He also has embarked on a campaign to persuade the Pennsylvania Legislature to enact a "Toxic Mold Protection Act," which would educate the public about the dangers of mold and set up standards for identification and remediation.

The cleanup has been painstaking, said Jim Mellon, president of Mellon Certified Restorations in Yeadon, Pa., which Clinton hired to do the work.

"Jobs such as this depend on the extent of the mold," said Mellon, whose two- to four-person crews have been working at the house since November. "The sources of the mold have to be located, the areas have to be contained, material removed under controlled circumstances, then vacuumed, washed and vacuumed again."

Drywall is porous, and if there is mold, it is all over the place. Hard furniture such as tables can be cleaned, but soft furniture such as couches have to be gotten rid of. "Air tests are taken before the job begins and after we are finished," Mellon said.

Other homeowners have taken more dramatic steps to get rid of mold.

On Feb. 14, for example, Steve and Karen Porath of Foresthill, Calif., set fire to their mold-contaminated house and their possessions. The couple, who blamed toxic mold for their children's illnesses and learning disabilities, lost about $90,000, including the $7,000 spent getting the house ready to burn.

"If you removed everything that could contribute to mold growth in a house, you'd be left with the foundation and asphalt shingles on the roof," ATC Associates' Watson said. "Unfortunately, everything that makes living in a house so pleasant is equally pleasant to the mold."

Clinton's homeowners insurance has paid only $6,000 of his remediation bill, he said, even though the insurer, whom Clinton is suing, sent in experts who confirmed the presence of black mold.

Insurers have become understandably nervous about toxic mold.

A jury in June awarded $32 million to a Dripping Springs, Tex., family, agreeing that Farmers Insurance Co. mishandled the family's homeowners claim for black-mold damage. The family had argued that Farmers failed to adequately and swiftly cover repairs for a water leak, allowing Stachybotrys to overrun their house and damage their health.

In response to this case and others, Farmers, State Farm and Allstate, Texas's three top insurers, stopped writing comprehensive homeowners policies there, even after the insurance commissioner imposed a cap on mold claims on standard policies at $5,000. Allstate began offering a lower-cost alternative policy in Texas that excluded mold.

Mold lawsuits have skyrocketed in California in the past two years. Insurance premiums rose about 20 percent last year, which insurance department officials attribute to "mold or fear of mold."

One law firm alone is handling more than 1,000 cases, including a highly publicized suit involving movie heroine Erin Brockovich.

In response, the California State Assembly passed a law requiring landlords and sellers of both residential and commercial property to disclose the existence of mold to potential tenants and buyers. The seller's transfer-disclosure statement, a requirement in real estate transactions since 1985, will now include mold.

Can a routine home inspection detect the presence of mold? Although a lot of it is hidden, "there are telltale signs that a home inspector is trained to locate," said Rick Ray of Montco Pest Control in Montgomery County, Pa.

A musty smell is one indication, but inspectors should check the top floor for a leaky roof as well looking for obvious signs such as discolored walls or wet areas underneath sinks, he said.

The Arizona Department of Health Services, noting that "there are a few available standards for judging what is an acceptable quantity of mold," worries that a lot of people who shouldn't be involved in mold inspection and remediation are.

Will Humble, a state epidemiologist, cited a newspaper recruitment ad by a company looking for mold inspectors.

The headline read: "Mold is gold."

Chris Clinton, with his wife, Cynthia Lucania, and sons Dylan and Noah, is spending more than $100,000 to get rid of mold in their Chalfont, Pa., home.