While you can’t do that for yourself, you can with your children. In the womb, babies automatically share their mother’s antibodies, which cross the placenta. This antibody donation can continue after birth through breastfeeding.
Breast milk is chock-full of immune-boosting ingredients. There is lactoferrin, for instance – a protein that inhibits the growth of bacteria – and sugars that block bacteria from binding to the body’s cells. Breastfeeding reduces infection rates, particularly in the developing world.
Some childhood diseases, though, are caused by immune defences going into overdrive, including asthma, eczema and allergies to pollen or foods. We know that children are less likely to get such allergic conditions if they grow up on farms or have pets, lots of siblings or spend time in daycare.
The hygiene hypothesis says that allergies are on the rise in the west because these days children aren’t exposed to enough germs. “If your environment at an early age is too clean, you’re not developing cells to respond to it,” says Arne Akbar, an immunologist at University College London. While no one is suggesting neglecting basic hygiene, the general advice is to “let kids be kids”, and allow them to play in the mud.