MISSISSIPPI STATE -- The cleanup after Hurricane Katrina has been a messy, smelly job, and for some people with allergies or respiratory problems, it can be a dangerous job.

Mold is taking hold across the affected region, lurking under wet flooring, penetrating walls, entering cars, and covering the contents of damp closets and storage areas. Dust is being stirred up as new construction and renovation is under way, and as people clean mud and dirt out of homes and businesses.

Jane Clary, health promotion and health education specialist with the Mississippi State University Extension Service, urged people returning to water-damaged buildings to make sure the air they breathe is safe.

"Most of the time, you do not need to wear a mask if you are collecting belongings or doing basic cleanup in a previously flooded home or building," Clary said. "Make sure you are working in a well-ventilated area, and try not to stir up too much dust or mold."

People with asthma, allergies or other breathing conditions are most at risk from mold. Those with a suppressed immune system such as cancer patients taking chemotherapy or those who have had an organ transplant also should avoid exposure to mold.

"Mold sensitivities can exhibit symptoms such as a stuffy nose, irritated eyes, wheezing or skin irritation," Clary said. "Look for signs of mold such as discolored walls or ceilings and a musty or earthy smell."

Remove porous items in water-damaged buildings. This includes flooring, furniture, clothes, drywall, insulation, ceiling tiles, paper and wood. Clean surfaces that can be salvaged with a detergent and water solution to prevent mold. Prevent water from re-entering the structure by covering holes in the roof and walls.

Wear protective eye wear, gloves and washable clothes when cleaning. Wash these clothes before wearing them again. Clary said to block off areas being cleaned with plastic sheets so mold spores do not spread to other areas.

The Centers for Disease Control and Prevention recommends removing mold growth with commercial products designed for this purpose or a solution of 1 cup of bleach in 1 gallon of water. On rough surfaces such as concrete, remove the mold with a stiff brush.

"If you choose to use bleach to remove mold, never mix bleach with ammonia. Mixing bleach and ammonia can produce dangerous, toxic fumes. Open windows and doors to provide fresh air and wear non-porous gloves and protective eye wear," the CDC recommends on their Web site.

When entering a wet building to begin work, open doors and windows and let clean air flow for at least 30 minutes before attempting to work indoors.

Wet mops or vacuums can limit the amount of dust stirred airborne, and can make breathing easier in a work area. If a respirator is needed, the CDC recommends an N95 respirator.

This respirator has been given federal approval and "can give you some protection from dust and mold in the air," the CDC states on its Web site. "They must fit well and be worn correctly to protect you."

Clary said quality respirators can be purchased in safety supply stores and in most home goods and hardware stores.

"If you ever have difficulty breathing, even while wearing a respirator, stop working immediately and move into clean, fresh air," Clary said. "Get immediate medical help if airways begin to constrict or your breathing becomes labored."

Respirators are rarely needed outdoors, but those with respiratory difficulty should observe their doctor's directions.

The CDC offered several tips to follow when cleaning and drying out a damaged home. Have an electrician check out the building's wiring before turning on the power to a structure with standing water. Use pumps and shop vacuums to remove standing water, and open doors and windows to allow air to circulate and dry wet areas. Fans and dehumidifies can speed this process.

"Have a professional check and clean the heating, ventilating and air-conditioning system in the building before you turn it on," Clary said. "A flooded HVAC system can grow mold and spread it throughout the entire home or building. A professional cleaning will kill the mold and prevent it from returning later. Once the air conditioning system is safe to use, turn it on to help remove excess moisture."