17/01/2017 3:00 PM AEDT | Updated 30/01/2017 10:18 AM AEDT

Science Says To Put A Frozen Drink In Your Kids' Lunchbox

Also, it's time to ditch the brown paper bag.

Janie Barrett / Fairfax Media
Not all lunches are made the same.

Eating sweltering sandwiches from sun-baked lunchboxes may be an Aussie school rite of passage but it's also a serious health risk.

Bacteria grows in warm food, and NSW Food Authority has researched whether adding a frozen drink bottle or brick to a lunchbox makes for a safer lunch.

The study pitted a brown paper bag, a plain lunchbox, and a lunchbox with a frozen drink or brick against each other on a 25-degree day.

Each lunch had an identical sandwich packed and was left in a shady spot for five hours.

They then sent the sandwiches off for bacterial analysis and found:

KidStock via Getty Images
Sorry, Stacey, your lunch is hot and gross.

The brown paper bag sandwich and normal lunchbox both had 14 times the bacteria it started with;

The lunchbox with a frozen brick had ten times' the starting bacteria; and

The lunchbox with a frozen drink had the least bacteria -- three times' its starting point.

The study also showed the lunches without a frozen element got 12 degrees hotter than the lunchbox with the frozen drink.

Food Safety Information Council chair Rachelle Williams said they needed to get the word out to parents.

"Bacterial growth is much slower in school lunch boxes if a frozen water bottle or ice brick is included," Williams said.

Lunch safety tips

1. When buying lunchboxes choose ones that have room for a frozen drink or freezer block and are easy to clean and dry.

2. Always wash and dry your hands thoroughly before preparing food.

3. Wash all fruits and vegetables thoroughly.

4. Make sure lunchbox foods are always well separated from other foods in the refrigerator, particularly raw meats, chicken and fish.

5. Keep the lunch cool in the fridge until you are ready to leave home.

Source: Food Safety Information Council

"Our research shows that 94 per cent of households with children pack school lunches, but a quarter of those don't include an ice brick or frozen water bottle. We urge parents to simply add one to keep their children's lunch safer."