PITTSBURGH -- According to the EPA, indoor air is more polluted than outside air. Many people are turning to air purifiers to help clean the air inside their homes.

But do they really work?

A few residents in Julie Burgo's Oakland neighborhood like to burn wood in their fireplaces.

The only problem--the smoke from those fires seeps into Burgo's older home through cracks around doors and windows.

This past winter was especially tough for her.

"I started getting these big circles under my eyes. In November I was in ER and found out I had asthma. I never had asthma in my life and all of a sudden, now I'm on two inhalers," Burgo said.

Burgo isn't the only family member affected by the smoke.

It has also caused problems for her mother who is on oxygen.

In attempt to clear the air, Burgo bought five room air purifiers.

She thinks they help somewhat when there isn't much smoke, but when the smoke is really thick it overpowers the purifiers.

Many experts say it's hard to prove whether buying air purifiers is worth the money.

Many people suffering from asthma and allergies turn to air purifiers to relieve their symptoms.

Many experts, including the American Lung Association, say there just isn't enough evidence yet to prove they are effective in relieving allergy and asthma symptoms.

In fact, many Pittsburgh allergy doctors do not recommend them to patients.

It may not be known for sure if air purifiers work, but there is evidence some are actually harmful because they emit dangerous ozone into the air.

Jonathan Nadle, an energy efficiency expert with Conservation Consultants and president of the Group Against Smog and Pollution (GASP) said ozone can make asthma symptoms worse.

"It's great up in the ozone layer, but not so good down here. It's an irritant, lung irritant, not something that's healthy to breathe," Nadle said.

Electronic air cleaners and ion generators are the kind that may produce ozone.

Nadle said, "Electronic precipitators have a high current that goes through a plate and generates charged particles and that captures the pollution. Some do put out a small amount of ozone."

But how small of an amount of ozone is safe?

Right now there is no standard for indoor ozone levels.

The EPA does have a standard for ozone emitted from medical devices.

That is 50 parts per billion (ppb).

The EPA warns that even low levels of ozone can cause symptoms like chest pain and shortness of breath and it may also make asthma symptoms worse.

Air purifiers that use a filter do not produce ozone.

According to Consumer Reports, they do cost more per year for electricity and replacement filters.

Prices for portable air purifiers can range from less than a $100 to $800.

If you have forced air heating, Consumer reports says you may want to try a whole-house system.

But before spending money, the experts said try some inexpensive ways to reduce the source of the pollutants in your home.

The American Lung Association says this can often be more effective than air purifiers.

According to Nadle, "One of the ways to reduce indoor air pollution is by getting a better quality of filter."

Nadle said a pleated paper furnace filter is good and only costs about $10.

Others ways to improve indoor air:

-Keep pets out of bedrooms. -Ban indoor smoking. -Remove carpet and other dust mite havens -Make sure bathroom, kitchen, and electric dryers are fan vented to the outdoors. -Vacuum frequently.