Cold and flu season in Australia coincides almost exactly with the driest indoor air conditions of the year—southern states run heating systems from May through September, the same months influenza and common cold viruses circulate most widely. This is not coincidental: dry air both dries out the respiratory tract, making it more vulnerable to infection, and helps airborne virus particles remain viable for longer. A humidifier addresses both mechanisms.

How Humidity Affects Cold and Flu Symptoms and Transmission

Research published in PLOS ONE (2013) found that influenza virus viability drops significantly as relative humidity rises from very dry to moderate levels. At 23 percent relative humidity, 70-77 percent of viral particles remained infectious after one hour; at 43 percent relative humidity, only 14-22 percent remained infectious over the same period. This makes maintaining 40-60 percent indoor humidity a genuinely useful measure for reducing airborne transmission risk within a household during cold and flu season, alongside standard hygiene practices.

For symptom relief once someone is already unwell, humidified air thins mucus secretions, easing nasal congestion and making coughs more productive rather than dry and irritating. This is the same mechanism behind decades of paediatric advice to run a humidifier or steamy shower for a congested child, and it applies to adults as well.

What a Humidifier Does Not Do

A humidifier does not kill the cold or flu virus itself, shorten the underlying infection, or replace medical treatment for moderate-to-severe illness. Its role is supportive: easing breathing and congestion symptoms while the immune system does the actual work of clearing the infection. Seek medical advice for high fever, difficulty breathing, or symptoms lasting beyond the typical course of a cold or flu.

Cool Mist or Warm Mist for a Sick Room?

Either type effectively raises humidity and eases congestion; the traditional preference for warm mist "vaporisers" during illness is largely about comfort and the psychological association with steam inhalation rather than any proven superior medical benefit. Cool mist ultrasonic humidifiers are generally the safer choice, particularly around children, since they carry no burn risk from hot steam or heating elements and operate more quietly, which matters for someone trying to rest. Warm mist units do offer one practical advantage: many include a medicated inhalant cup for products like Vicks VapoSteam, which some people find eases symptoms further—check with a pharmacist regarding age-appropriateness for children before using inhalant products.

Extra Cleaning Precautions During Illness

When running a humidifier for someone who is unwell, daily tank emptying and rinsing becomes even more important than usual, since a humidifier tank already provides ideal conditions for bacterial growth, and you do not want to introduce a secondary respiratory irritant on top of an existing illness. Follow the standard daily and weekly cleaning schedule, and consider using distilled water during illness periods specifically to minimise any additional particulate the person is breathing in while their respiratory system is already compromised.

If the humidifier is being used in a child's room during illness, the same nursery safety rules apply as in ordinary use—cool mist only, positioned at least a metre from the cot or bed, and no medication or inhalants added directly to the water tank unless a paediatrician specifically advises it. See our full babies and nurseries guide for detailed placement and safety guidance.