Q: How can I clean mold off walls?

A: Your question prompts many more. How much mold are you dealing with? Is it just on the paint or tile, or is it embedded in drywall? Do you have any underlying health issues that warrant extra caution? And do you know why the mold has appeared and what to do to keep it from returning?

Much has been written about serious mold problems and the health consequences. These concerns are valid. But it’s also important to keep things in perspective. You probably don’t need a hazmat team to come in to clean a one-square-foot patch of mold off a wall.

The Environmental Protection Agency suggests about 10 square feet — about 3 by 3 feet — as a gauge for determining what homeowners can probably clean up themselves with basic safety measures vs. what needs professional-level protocols, whether by the homeowners or by a professional remediation team. This threshold was set because of an understanding of what makes mold — and mold cleanup — a risky endeavor from a health standpoint. Mold and mold spores are allergenic, and some molds are toxic. This is true whether the mold or the spores are dead or alive, which is why the EPA does not generally recommend using chlorine bleach or other biocides as part of mold cleanup. The chemicals pose their own health risks without a health benefit.

Paint companies, which often recommend scrubbing away mold with a solution of bleach in water, have a different perspective. Their interest is in making sure a new coat of paint sticks and doesn’t immediately start growing mold or mildew. So they recommend using bleach as a way to sanitize the surface, although what’s not usually stated is that, unless the new paint goes on as soon as the wash water dries, it won’t necessarily guarantee that new, live spores haven’t taken up housekeeping on the surface in the interim.

Whether you include bleach or other biocides as part of your routine, it’s important to recognize that mold can cause allergies if you get it on your skin or in your eyes, or if you inhale the spores. To clean up even small areas, the EPA recommends wearing rubber gloves, goggles and a mask labeled as an N95 respirator.

If the mold is on a hard surface, which includes paint on a wall, use a cloth or sponge dampened with water, or water mixed with a little detergent, to wipe it off. Rinse out the cloth or sponge and wipe again.

If the surface is stained and will stand up to bleach, or if you plan to repaint and are following instructions from the paint manufacturer, wipe the cleaned surface with a diluted bleach solution. Use 1 part bleach to 3 parts water, according to Sherwin-Williams. If you don’t want to use bleach but do want something other than water, try vinegar, borax or branded products that you can find at a hardware store or home center, which also kill mold. Even if you do sterilize the surface, though, enough mold spores are always floating around in the air that mold can regrow if the conditions are right.

If the mold is on a porous surface, such as ceiling tiles or unpainted drywall, there is no way to completely get rid of it. You will need to remove and replace the moldy material. Besides making this a much more complicated job, removing contaminated material also greatly increases the risk of stirring up mold. Switch off and seal vents for heating and air conditioning, and try to create negative air pressure in the room. Pros do this by taping up plastic sheeting and setting up an exhaust fan to pull room air out through a window.

For a relatively small job in a small room, you might just clear out the room (so you don’t have to decontaminate everything later), close the door and switch on a box fan in a window. Tape up cardboard to seal around the fan, so fresh air doesn’t come in from the window; you want the fan to be pulling air from the rest of the house through gaps around the door, ensuring that air in the room doesn’t get into the rest of the house. Wear clothes you can toss, and bundle up all the debris before you open the door.

Whether the mold is on porous or nonporous surfaces, probably the most important aspect of cleanup is preventing the mold from reappearing. One of the key conditions that allows mold to flourish is moisture, which can form on surfaces because of a water leak or because of condensation from warm, humid air hitting a cold surface. If there is a leak, you need to fix it. The remedy for condensation, though, isn’t always as obvious. If the mold grew on a wall in a closet in a cold corner of your house, try increasing ventilation by clearing out clutter and leaving the door slightly ajar. Desiccants can also be helpful.

If the mold is on a bathroom wall, consider upgrading your exhaust fan — and make sure it vents to the outdoors, not the attic. To boost airflow to get shower steam out of the room, try leaving the door slightly open while you shower. And consider adding a timer switch to the fan, so it stays on for about five minutes after your shower ends. Wiping down shower walls can also help lower the amount of moisture in the room; use a squeegee or a microfiber cloth that you can wring out.

A damp basement or crawl space can lead to mold problems throughout a house, not just under the floor, because of the way air and water vapor move. A dehumidifier can help, or you may need to install a basement waterproofing system or cover the dirt in a crawl space with plastic. This Old House has a good overview in an article titled “Wet Basement Solutions: How to Stop the Leaks From Coming” on thisoldhouse.com.

Especially in a bathroom, where moisture is always an issue, it can be helpful to repaint with a product formulated to resist mold or mildew growth on the paint surface. Sherwin-Williams, for example, includes antimicrobial ingredients in its Emerald, Duration and Harmony lines. As extra insurance, you might want to prime first with Zinsser Mold Killing Primer ($14.99 a quart at Ace Hardware), which is registered as a fungicide and can kill spores on the surface, negating the need to wash first with a bleach solution.

Have a problem in your home? Send questions to localliving@washpost.com. Put “How To” in the subject line, tell us where you live and try to include a photo.