The mercury isn't the only thing that rises during a heat wave.

Experts say tempers flare and suicide rates increase during hot, steamy summer months.

Patricia Sasseville owns Unique Roofing in Windsor, Ont., a city where temperatures have reached 37 C and humidex readings nearly 50 C. Her crew starts at 6 a.m. and by noon, her employees can sometimes be at each other's throats.

“We get edgy with each other. The heat gets to your brain. Temperatures rise outside and temperatures rise with each other,” she said.

“The littlest thing sets you off,” said Fernando Munoz, who works for Sasseville.

While some people may just become crabby and irritable in the heat, it leads to much dire consequences for others.

Dr. Len Cortese said it's common for psychiatric beds to fill up during heat waves.

Right now the mental health unit at Windsor Regional Hospital is completely full.

"Essentially, what's occurring is that the neurotransmitters, the chemicals in the brain, are probably going off balance. When chemicals in the brain go off balance, it will cause difficulties in what the brain does," he explained. "And what the brain does is, it helps us with our mood, so our mood is set off. The brain helps us keep our anxiety under control so [during heat] people have difficulties with anxiety."

According to the Canadian Mental Health Association, late July and August have the highest suicide rate out of all the months of the year.

"During heat waves there's an increase in suicide, and there's an increase in aggressive behaviour," Cortese said. "Again, it's the stress of the heat that's affecting the brain."

Cortese said focusing on doing things you enjoy is key to keeping your temperature and temper under control.

Heat also makes people tired — even when they aren't overly exerting themselves.

Kevin Milne is a kinesiology professor at the University of Windsor. He said there is a scientific reason why an afternoon siesta is popular in some parts of the world.

"As you get hot, your central nervous system tends to get depressed. But that's not depression. It just doesn't work as hard, so you feel fatigued," he said. "And that's why people tend to feel lazy on hot days."