Experts have warned that children are at risk of taking toxic lunchboxes to school, because parents aren’t taking enough care during their preparation.
Boffins found that up to 90 per cent of surfaces touched during preparation of a simple meal, such as a child's school sandwich lunch, can become infected with bacteria from food.
They discovered that contact from raw meat on objects such as knives, chopping boards and tea towels caused dangerous levels of contamination.
These surfaces then spread bacteria onto ready-to-eat foods and into children's lunchboxes - increasing the risk of illnesses such as e.coli.
Less than half of mums questioned in the study claimed to clean their child's lunchbox daily.
Prof John Oxford, chairman of the Hygiene Council and professor of virology at Barts and The London School of Dentistry, said: "Food poisoning can cause serious illnesses.
"Bacteria such as e.coli have been a major cause in recent food associated outbreaks.
"However simple hygiene measures can protect you and your family from infection.
"Washing your hands with soap after touching raw meat and vegetables is vital, as is disinfecting food and hand contact surfaces such as chopping boards and fridge door handles.
"The study shows that dish drying towels and cleaning cloths are also responsible for spreading contamination around the kitchen and these should be washed at high temperatures or disinfected regularly to break the chain of infection."
The estimated number of child-related parental sick leave days reached 190 million last year, at a cost of £17 billion to the UK economy.
Mums participating in the research were asked to prepare a range of meals - including a child's lunch box, which showed the high levels of contamination.
Items affected included chopping boards and knives, which were found to be contaminated in 92 per cent of cases.
The dish drying towels, kitchen cleaning cloths and sponges were also found to be highly contaminated.
Volunteers used these to wipe their hands after touching raw chicken and vegetables and then again to wipe hands and surfaces - and even to dry grapes.
The study found just 45 per cent disinfected surfaces at home regularly - despite the practice being important in limiting the spread of infection.
The research, backed by cleaning firm Dettol, discovered none of the volunteers washed their hands after touching raw vegetables and salad or washed all of the salad items.
Results showed that only 26 per cent of mums know that raw vegetables can also be a source of food poisoning bacteria.
Although 49 per cent of mothers said their child was made to wash their hands before lunch, 55 per cent didn't wash the fruit and veg before putting them into the lunchbox.
Almost three quarters (73 per cent) also did not refrigerate it once prepared.
And despite the potential for cross contamination of lunch boxes - just two per cent of mums consider them to be a carrier of the most bacteria at school.
Professor Oxford said: "The kitchen is a hygiene hotspot and proper food storage, preparation and cooking are very important for preventing foodborne illness, especially as children head back to school.
The Hygiene Council's top five tips for a hygienic packed lunch:
- Clean and disinfect the kitchen work surfaces with antibacterial sprays and wipes. Wipes can be disposed of immediately after use.
- Wash fruit, salad and vegetables thoroughly - especially if they will be eaten raw
- Freshly prepare food each day where possible but if you have to store packed lunches overnight, check labels to ensure you store foods at the right temperature
- Check that your child can store their food somewhere cool until lunchtime or consider using a freezer pack or cool bag to help keep your child's lunch chilled
- Try to get your child into the habit of washing their hands regularly with antibacterial soap, particularly after visiting the toilet and before eating, both at home and at school.