Some house cleaning service workers breathe in double the formaldehyde levels considered safe.

Clean your shower stall for just 15 minutes with products containing glycol ethers -- a toxic air pollutant common in house cleaning products -- and you could be exposed to three times the recommended exposure limit for one hour.

Combining the use of an air freshener with an ozone-generating air cleaner and you could expose a child to formaldehyde levels 25 percent greater than California recommends.

Cleaning your home can be very hazardous to your health.

So says a new study, four years in the making, "Indoor Air Chemistry: Cleaning Agents, Ozone and Toxic Air Contaminants", produced for California's Air Resources Board at the California Environmental Protection Agency by the Department of Civil and Environmental Engineering at the University of California-Berkeley, and the Indoor Environment Department of the Lawrence Berkeley National Laboratory.

"While effective cleaning can improve the healthfulness of indoor environments, this work shows that use of some consumer cleaning agents can yield high levels of air pollutants, including glycol ethers, formaldehyde, and particulate matter. Persons involved in cleaning, especially those who clean occupationally or often, might encounter excessive exposures to these pollutants owing to cleaning product emissions," the study says.

Without actually naming the products, the report measures the dangers of incorrectly using common household cleaning products and highlights the health risks associated with inhaling their polluting toxins.

Researchers purchased 21 household cleaners from East San Francisco Bay Area stores, often selecting products with "fresh scent" claims. Six contained the glycol ethers and 12 contained terpenes. Researchers purchased general-purpose degreasers and cleaners; glass and surface cleaners; anti-bacterial sprays and deodorizers; floor cleaners; furniture cleaners and polishes and air fresheners.

Of concern are products that contain ethylene-based glycol ethers and terpenes, compounds extracted from plant oils to infuse cleaners and air fresheners with that fruity, lemon, pine, or other "clean" scent.

The study says terpenes mix with ozone in the air and generate formaldehyde, a known carcinogen. A host of unwanted health effects can ensue after using the products ranging from mild respiratory irritation to acute asthmatic and allergic reactions.

The study says the cleaning products can be safe when used properly and offered the following advice.

• Beware of marketing that comes with unsubstantiated claims of environmental superiority or "green" claims and go for scent-free cleaning agents.

• Follow use instructions and don't use more of the cleaning agent than necessary to complete the job.

• Clean with adequate ventilation, during periods of low occupancy and allow adequate time (several hours) to ventilate the area after cleaning.

• Rinse cleaned surfaces; remove paper towels, sponges and mops from the cleaned area; rinse sponges and mops before storing.

• Don't use products with ozone-reactive elements on days when outdoor ozone levels are high.

• Avoid the use of ozone generating air cleaners, especially in the presence of cleaning products and air fresheners that contain ozone-reactive constituents.

"The research reported here suggests some simple measures that can be employed to reduce exposures to primary and secondary pollutants associated with cleaning products and air fresheners. Use products in dilute form whenever appropriate," the study says.

Information about safer, alternative household cleaners is available from "Safe Substitutes at Home: Non-toxic Household Products" and "Alternative Spring Cleaners: A Recipe for Good Housekeeping".