How an air purifier works: Do you really need one for your allergies? Can it filter out bacteria and

An air purifier, regardless of brand, price and design, typically has a fan to draw in air and a filtering medium to remove airborne particles, explained Dr Papia Sultana, a senior lecturer at the School of Engineering at Republic Polytechnic.

What sets one model’s performance apart from another is really the type of filter used, she said, and there are two broad categories: Mechanical and electronic.

“Mechanical filters use a fibrous medium coated with an odourless, adhesive substance, so that any particles that come into contact with the filter’s surface stick to it,” said Dr Sultana. Examples of such filters include the pleated, accordion-like high-efficiency particulate air (HEPA) filters as well as the ultra-low penetration air (ULPA) filters.

The electronic filter, on the other hand, is controversial. It uses electrostatic charge to sieve out contaminants such as dust, smoke and pollen. However, “most of these filters use high voltages, and there is the concern of ozone gas emission and its associated toxicity”, said Dr Sultana. Examples of electronic filters include electrostatic and ionised filters.

But isn’t ozone protective? Yes, in the upper atmosphere, where it filters out the sun’s damaging ultraviolet radiation, according to the United States Environmental Protection Agency. But in the atmosphere that we live in, even low amounts of ozone can cause chest pain, coughing, shortness of breath and throat irritation.