The Hygiene Hypothesis: Does Cleanliness Cause Asthma?

Also, several studies (like this one) showed that children exposed to pet dander (proteins in pet saliva and skin, but not pet hair) were less likely to develop asthma.  This seems counterintuitive, since it is common (and correect) advice for people and children with asthma and allergies to either get rid of their pets or to, at least, keep them out of the bedroom and off the furniture.

So why would this be?  Consider this: asthma is an autoimmune disease.  When we are born, our immune systems are still developing. Considering that our immune system doesn't fully mature until we are about 3 months old, it is prior to this time that something "might" occur to turn the so-called asthma gene on -- if a person has the asthma gene.

The hygiene hypothesis surmises that if we are not exposed to certain bacteria and parasites for our immune systems to battle, our immune systems get "bored" and may, instead, react to and create antibodies against normally harmless substances such as pollen and dust, i.e. allergens.

Once the asthma gene is turned on, you, more than likely, will have asthma. Many people will notice asthma symptoms in childhood as they are exposed to their asthma triggers.  However, many others will have symptoms so mild during childhood they won't even realize they have it until they are adults (adult onset asthma).

Per this hypothesis, there are people that may be at higher risk of developing asthma as well as events more likely to trigger its development, such as:

• Premature babies (they have immature immune systems)
• Respiratory Syncitial Virus
• Antibiotic usage in the first months (they kill normal bacteria as well as bad bugs)
• Children born by C-section (no exposure to bacteria in the vaginal canal)
• Not breast feeding (no exposure to bacteria from mom)
• Smoke inhalation
  
• Obese mothers (fat may hamper development of the lungs)
• Pregnant women breathing pollutants (may cause asthma in the womb)
• Stress

However awkward this sounds, it all makes sense to me.  What do you think?