'Feeling' a change in the weather

Over the weekend I received an email from Amy in Lena, IL wondering how the change in pressure can affect someone who has arthritis.  I'm sure we've all know and have heard someone say they can tell when the weather is going to change because the can feel it in their bones.  While there is no true correlation between the weather and the pain someone who has arthritis feels there are many theories as to how this can actually occur.  One theory, which seems to be the most common, is the fact that already inflamed tissue in the body surrounding the joints can swell even more and cause an increase in arthritis pain when the pressure drops.  It's almost as if the joints in our body are acting as a human barometer.  Just like the atmosphere is in a constant state of trying to balance itself out, the human body is trying to balance the equilibrium in body pressure.

To try and under this a little more and how air pressure tends to affect the pain some people may feel, we first need to look at the definition of air pressure.  Air pressure is the force exerted on any surface by the molecules composing air.  Basically it's the force, or weight, on a particular surface in the atmosphere.  Air molecules are important in this definition because the more air molecules you have above the surface of the earth the more pressure, or force, is exerted down causing the pressure to rise.  Example, think of when you inflate a bike tire or basketball.  The air pump causes the pressure inside the pump and object to rise - causing it to inflate.  Just the opposite can be said when there are fewer air molecules above the surface of the earth.  There is less force exerted towards the surface causing the pressure to decrease.

There have been several studies conducted to try and better understand the relationship, if any, between changing weather and the aches and pains someone may feel.  In many of the studies that were conducted it seemed as if an increase in pain was felt on cold and rainy days or afternoons where the humidity was higher.  These type of weather events typically happen when low pressure is occurring.  Air rises throughout the atmosphere when there is low pressure causing the surrounding air at the surface (which has a higher pressure than the low) to move in to try and replace the air that is lost.  It's that change in pressure that may make people with arthritis a little more sensitive to the surroundings of the atmosphere and cause them to 'feel' the changing weather in their bones.