Researchers at Warwick University in Coventry found that having a cat or dog exposed children to more infections early in life.

However, this exposure boosted their immune systems in the medium term and meant these children attended school more often, on average, than pupils who did not have pets.

Dr June McNicholas and colleagues tested the saliva of 138 children for the antibody immunoglobulin A (IgA), which is used as an indicator of immune system strength.

High levels of IgA suggest that the immune system is under strain while low levels show that it is vulnerable to infection.

Health benefits

The study showed that antibody levels among pet owning children were significantly more stable, indicating that they had robust immune systems.

Pet owning children were found to have an extra nine days at school over the course of the year compared to those without animals.

According to the researchers, the findings appear to support the so-called "dirty hypothesis".

It suggests that too much cleanliness early in life can leave the immune system weakened later on.

It has been linked to soaring rates of childhood asthma in recent years.

Dr McNicholas, a health psychologist who led the study, said: "Pet ownership was significantly associated with better school attendance rates.

"This was apparent across all classes, but was most pronounced in the lower school (classes one to three, aged groups five to eight).

"Here, the pet owners benefited from up to 18 extra half days schooling per annum than their non-pet owning counterparts."

However, Dr McNicholas warned that pets can also pose health risks to children.

One of the biggest risks is the roundworm Toxicara canis which infects dogs and can cause anything from stomach ache to eye damage.

Nevertheless, the Warwick University study found that despite these dangers three out of 10 children admitted sharing food with their pets while 21% let their pets lick their fingers.