[omid (OP)]

omid's biology book says while explaining asthma that

"there is also recent evidence that our cleaner lifestyle mean that we are now exposed to fewer allergens as chilren and therefore become more easily sensitised to them in later life"

what does it really means to explain cz this question came up in exam too and made omid so confused that omid doesn't think omid gona get full marks for this [:-'(] [:-'(] [:-'(]   




MOD EDIT - I've changed your title so that people are more likely to respond - Ben
 

[BenV]

It's been a while since I studied immunology, so forgive me if I'm wrong, but...

When you're young, your immune system is somewhat more plastic than when you're older.  Infants immune systems need to learn to recognise harmful pathogens from friendly or neutral agents.

As such, if you're not exposed to something when you're young and the system is still learning, it reacts to it as if it were dangerous.  This, in principle, can lead to an increase in allergies because instead of our immune system ignoring a neutral environmental agent, for example pollen, it responds as if it's under attack.

In the case of pollen, this gives us hayfever when our body responds by producing histomine.

So if we live a cleaner lifestyle, we'll be exposed to fewer antigens when we're young, and will be more likely to respond to them when we do encounter them - this is known as the Hygiene Hypothesis.

With illnesses like asthma and eczema (which you will frequently find together), innocuous environmental agents cause an immune response, which in turn can lead to the symptoms (an asthma attack or outbreak of eczema).

That's very broad and quite vague, but I hope it helps.  Someone more knowledgeable than me on these matters (RD perhaps?) may be able to fill in my gaps and improve my generalisations.

[RD]

RD perhaps?

I'd sidestep the question by posting a link to the hygiene hypothesis.  []

the hygiene hypothesis was developed to explain the observation that hay fever and eczema, both allergic diseases, were less common in children from larger families, which were presumably exposed to more infectious agents through their siblings, than in children from families with only one child.

http://en.wikipedia.org/wiki/Hygiene_hypothesis

There could be other explanations for this observation, e.g.
Persons who have heritable (auto)immune disease are less fertile than those who don't.
Or a pre-natal phenomenon (rather than a hygenic environment in early years) which is determined by the number of previous births, similar to this.

[omid (OP)]

omid knows the concept of the topic but this sentence doesn't really makes sense to omid [] [] []

"there is also recent evidence that our cleaner lifestyle mean that we are now exposed to fewer allergens as chilren and therefore become more easily sensitised to them in later life"