Parents should suck their baby's dummy to help protect them from allergies, according to new advice.
Mums and dads have also been told to let children eat food from the floor, take lots of walks in the countryside, visit farms and regularly kiss family members. Oh, and get a dog!
The advice comes from experts at Cambridge University and University College London who said that being too clean has killed beneficial bacteria, which keep the immune system strong.
Prof Graham Rook told the Cheltenham Science Festival that children whose parents sucked their dummies to clean them were a third less likely to develop asthma and eczema.
He said: "If the parents pick up the dummy right away and sterilises it or replace it with a new clean one, that child has a considerably greater chance of having eczema and asthma.
"But if you're the sort of parent that sucks it clean and it sticks it back in the baby's mouth, then it actually protects them from allergic disorders.
"It's because they have better bacterial development in the mouth and gut. And this is what protects them.
"We need micro-organisms from our family and the natural environment. Picking them up from birth, breast milk, kissing."
He said the rise in antibiotics, caesarean sections, processed food and unvaried diets have all contributed to a lack of healthy bacteria.
Figures released this week showed that the number of people admitted to hospitals with allergic reactions has leapt by eight per cent in 12 months.
It did not state exactly what triggered the reaction but the commonest allergies are for food - such as peanuts, milk and egg - drugs and insect venom.
Prof Rook claimed it was no coincidence that older generations had fewer allergies, because they were exposed to more microbes as children.
He said simple changes, such as spending more time outdoors in natural environments, and particularly around animals, could help rebalance the immune system.
He said: "Keeping a dog is definitely protective against having an allergic disorder. The bring more microbiotic diversity into the home. Even families who don't normally cuddle each other all cuddle the dog.
"Exposure to farms and pigs and cows are good. Exercise in the park and not in the gym."
But he warned against taking supplements to boost the immune system.
He said: "The immune system is a dangerous thing and the problem in the western world is our systems are trigger happy. The last thing you want to is boost the immune system.
"In many cases our immune system is going bonkers, trigger happy. You shouldn't have a flare up just because you've been exposed to some pollen or cat hair."
However Prof Rook said basic hygiene like hand washing was still important.
He said: "It is completely wrong to say that being dirty is good for you and stops allergies occurring. All it will do is make you ill.
"Hygiene protects you from bad things. Childhood infections do not prevent allergies, they make them worse.
"The bottom line is that we need more hygiene, but you need to be targeted."