Air conditioning is indispensable during summer in Shenzhen, but excessive and prolonged exposure to air conditioning may also be harmful, as a recent increase in air conditioning-related illnesses has shown.

"More patients came to hospital for cold and fever recently, many of them carried the diseases because staying in air-conditioned rooms for too long or with too low temperatures," said Wang Shuiyun, head of emergency section with the Shenzhen People's Hospital.

Wang said most patients complained of dizziness, low energy, headaches and loss of appetite after having stayed in air-conditioned rooms for a long time.

People are prone to catching colds or contracting respiratory diseases if room temperatures are set too low, or there is not enough fresh air.

The local center for disease prevention and control has recommended the difference between indoor and outdoor temperatures be less than 7 degrees Celsius.

"When it is hot, the pores of skin are open to adapt itself to heat while heat is discharged from the pores. The human body cannot cope immediately after entering a cooler room," said Wang.

In an investigation last year, the center found that among microbes near 170 air conditioner ducts in four and five-star hotels in Shenzhen, 75 percent contained legionaires' bacteria, which may cause acute respiratory diseases.

The test found that contaminated ducts and cooling towers of central air-conditioning systems are the main sources of the bacteria.

The center has reminded that air conditioners should be cleaned every year and people should open windows often and let in fresh air.

A doctor who gave his surname as Chen with a pet hospital in Nanshan District said pets, like human beings, can catch colds easily if exposed to air conditioning for too long.

"Dogs and cats have their own adjusting abilities. But if they stay in the draught of the air conditioners for long or frequent in and out of the rooms, they may get sick too," Chen said.

Editor: Yan