NSW Health executive director Dr Jeremy McAnulty said asthma patients should take extra care during the heat. 

“Ozone can irritate the lungs, so people with asthma need to follow their Asthma Action Plan and have their relieving medication with them,” Dr McAnulty said. 

“Ozone levels are higher outdoors than indoors, so limiting time outside during the heat of the day and in the evening helps people to keep cool and limit their exposure to ozone pollution.”

Read also:

Fined for eating while driving? Here are 10 lesser-known rules that attract heavy fines

NSW Health is also asking residents to watch out for any symptoms of measles after a Sydney man was diagnosed with the contagious illness.

He had returned from Thailand and is suspected to have contracted the disease during his travels.

The man is said to have recovered from the infection.

Read also:

Heatwave: NSW Health's tips for staying healthy during hot weather

NSW Health director of communicable diseases, Dr Vicky Sheppeard, said measles symptoms include fever, sore eyes and a cough followed three or four days later by a red, blotchy rash spreading from the head and neck to the rest of the body.

“The time from exposure to the disease to the onset of symptoms is typically about 10 days but can be as long as 18 days so people [in Sydney] should be alert to symptoms until January 14,” Dr Sheppeard said.

NSW Health issued an advisory earlier this week asking holidaymakers travelling to South East Asia to be aware of new health risks.