You can be quite a long way from a bushfire and still have it affect your health.

Bushfire smoke can travel hundreds of kilometres and it poses a range of health issues — especially for those with pre-existing heart or lung conditions.

And because bushfire smoke can cover large areas, including major cities, it has the potential to affect millions of people, according to Martine Dennekamp, an adjunct epidemiologist at Monash University.

"Research has shown that air pollution from bushfires is associated with effects on the lungs and the heart," Dr Dennekamp said.

"For example, research in Victoria found a link between out-of-hospital cardiac arrests in Melbourne and bushfire smoke."

These cardiac arrests occurred several hundred kilometres away from where bushfires were burning in the Victorian Alps.

What's in bushfire smoke that makes it a health risk?

Bushfire smoke is a mixture of water vapour, small particles and gases, which may include carbon monoxide, carbon dioxide and nitrogen oxides.

These gases travel long distances and are known to irritate the respiratory system, but evidence suggests it's the particles that are most damaging to people's health, according to NSW Health.

The smaller and finer the particles, the more damaging they can be because they're able to travel deeper into the lungs, Dr Dennekamp said, with particles smaller than 2.5 micrometres likely to cause the most significant concern.

Symptoms caused by these particles can continue for days after they are inhaled.

Who is at risk?

Those most likely to be affected by bushfire smoke include:

People with existing heart or lung conditions, such as asthma, chronic obstructive pulmonary disease and chronic bronchitis

People with existing heart or lung conditions, such as asthma, chronic obstructive pulmonary disease and chronic bronchitis Pregnant women

Pregnant women Older people

Older people Young children

Environmental health expert Fay Johnston from the University of Tasmania said it was important for all of these people, especially those with heart and lung conditions, to monitor their symptoms when exposed to smoke and for some days after.

How does smoke affect you?

Those in high-risk groups are going to feel any effects of bushfire smoke more than the general population.

"If you can see it or smell it then that means there is a significant amount in the air and people in high risk groups would be advised to try and minimise their exposure," Dr Johnson said.

For instance, people with asthma may experience wheezing, coughing, chest tightness, and difficulty breathing while the smoke is around and for some days after.

Healthy people tend to tolerate being exposed to this type of pollution, although it can cause itchy or burning eyes, throat irritation, runny nose and some coughing. But these symptoms usually pass once the person is no longer exposed to the smoke.

What can you do to reduce your chances of being affected?

For those in areas affected by bushfire smoke, but not under direct threat from the fires, experts recommended the following precautions to reduce the health effects.

Stay indoors

Staying inside will reduce your risk of inhaling small particles. ( Getty Images: Hero Images )

The best way to avoid breathing in bushfire smoke is stay inside with the windows and doors closed, preferably in an air-conditioned building.

Particle levels are likely to be higher outdoors than indoors, so people sensitive to fine particles should limit the time they spend outside.

Keep an eye on your local air quality by checking your local environment monitoring agency's website for advice.

Set air conditioning on recycle

Avoid bringing smoky air into your house. If you have the option of adding a filter to your air conditioner, do so.

But take advantage of periods of clean air to ventilate your home, as smoke still penetrates indoors and can take time to disperse unless the house is opened up.

Consider a portable air filter

Portable air cleaners, available from home electrical stores, will lower the concentration of indoor particles and reduce the risk of health impacts from smoke. They will work best in a well-sealed room.

Dr Johnson recommended air cleaners with a HEPA filter to provide protection from particles.

"Devices that only humidify, generate negative ions, or absorb unpleasant smells do not reduce airborne particles," she said.

Avoid physical activity outside

Dr Johnston said it was a good idea to avoid exercising outside when you can see smoke in the air.

"If you run or do physical activity you breathe in a lot more because you need to get a lot more oxygen in, so your ventilation increases 10-fold and that means you are increasing your pollution exposure 10-fold."

Keep medication on hand and follow a treatment plan

People with asthma — and other health conditions — need to make sure they have any medication they need on hand at all times.

The Victorian health department recommends having five days of medication on hand. Those an asthma action plan or other treatment plan should continue to follow it.

If your symptoms get worse, seek medical advice.

Wear a mask

Certain types of masks can protect you from smoke particles, but they need to fit correctly to be effective. ( Flickr: Ian Sane )

NSW Health Department says wearing a P1 or P2 mask (available at hardware stores) properly fitted over your mouth and nose will filter fine particles and minimise the effects of bushfire smoke.

But Dr Johnson said these masks weren't a failsafe.

"They give some protection against smoke particles but are only effective if worn correctly with a good seal around the mouth and nose; they can make it harder to breathe and they do not filter out gases," she explained.

"Simple paper or cloth masks do not provide protection."

Leave the area

If the smoke continues for some weeks, or if a person's health means they're at higher risk because of smoke exposure, consider staying with friends or relatives outside the smoke-affected area.