The five-second rule

Five second rule.
Some physicians think decreased germ exposure in early childhood and increased rates of asthma and allergic diseases are connected.

Every parent has his or her version of the five-second rule: The length of time you’d let a pacifier or snack or toy sit on the ground before you feel compelled to rinse it off or throw the item away.

Practicing the rule – that is, not tossing the item in the trash or giving it back to your child without washing it – is usually accompanied by a few furtive glances to see if anyone else witnessed this failure of parenting. Occasionally, a parent merely pops the item in his or her mouth in lieu of washing – and then hands it back to the child.

We’re all guilty of doing this. But now, some recent studies may make you feel better about it.

Rise in childhood asthma

Rates of asthma and other allergic diseases have been rising significantly over the past few decades. About one in 10 children suffers from asthma, and it is the number one chronic condition affecting children. It is also the top reason kids miss school and the third highest cause for childhood admission to a hospital.

Some scientists hypothesize that as rates of cleanliness have increased, young children have been less exposed to germs early in life, particularly in their GI tract and lungs. This is significant because the GI tract and lungs are important to the maturation of the body’s immune response and the possible development of illnesses caused by overactive immune responses – such as allergies and asthma.

Some physicians think there is a connection between decreased germ exposure and increased rates of these illnesses.

The hygiene hypothesis

Children in settings with presumably higher exposure to dirt and germs tend to be less likely to develop asthma and allergic diseases

  • Kids raised on farms have lower rates of asthma and wheezing.
  • Kids from families with larger numbers of siblings have lower rates of hay fever and allergic skin conditions.
  • Early attendance at day-care reduces the risk for asthma in high-risk children.

The “hygiene hypothesis” suggests our tendency to sanitize everything around our newborn has contributed to the rise of these conditions because children aren’t exposed to enough germs. 

During pregnancy, settings in the fetal immune system help protect the fetus from being rejected by the mother’s immune system. But after birth, the newborn’s immune system needs to be challenged so it can develop effective responses against disease and infection.

The goal of challenging the immune system by exposing it to germs is to make sure the cells of the newborn switch to protecting itself and don’t turn against some of its own tissue, leading to the development of inflammatory diseases. Without adequate exposure, a child may be more susceptible to developing allergic skin conditions, asthma, or inflammatory bowel disease. 

Some people support vaginal seeding, the practice of exposing babies born by cesarean section to germs found in vaginal secretions of the mom, for this reason. Scientists have shown you can at least partially mimic the effects of being born vaginally on bacteria living in an infant’s GI tract and skin by this technique – but more research is needed to show that this has a healthy impact on the child’s development.

Taking a closer look – in mice

Mice can provide us with some clues as to how this process works in our own immune systems. 

Mice have natural killer cells found in the lining of the GI tract and lungs. These cells are important for fighting off infection, but in higher numbers they may also turn against the body’s own tissues and contribute to the development of diseases such as inflammatory bowel disease and asthma.

Who knew scientists could raise “germ-free” mice? But they can. And if scientists wait until adulthood to expose germ-free mice to germs, the mice develop higher rates of a form of inflammatory bowel disease and allergic airway disease, which is similar to asthma in humans. These mice have higher levels of the natural killer cells for life.

However, if those same mice are exposed to germs immediately after birth, the levels of killer cells drop and the mice do not develop colitis or reactive airway disease. Germ-free mice exposed to bacteria shortly after birth tend to be healthier for their entire lives.

Results from studies involving mice do not always apply to humans. But the idea that some germ exposure is good – even mandatory – for a healthy start in life is intriguing.

Not all germs are created equal

I want to make this clear – I am not suggesting infants should be exposed to all types of bacteria. Certainly, there are many, many disease-producing bacteria (like pertussis) that are dangerous for children.

But for common, more harmless bacteria, perhaps early exposure doesn’t pose quite the risk new parents imagine. And maybe the five-second rule can be relaxed a little more.

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