.  All my life I have heard about the fact that the outer layer of your skin is made up of dead cells.  These dead cells are your first line of defense against germs, harmful chemicals, etc.  It is one thing to hear about this dead skin, but it is another thing to actually see it.  I happened to be sitting in a beam of light when I scratched my arm and immediately knew what I would do for this weeks experiment.  You will need:

•  a dark room with a window
• a sunny day
• you
  
    Close the curtains, leaving just a narrow slit for light to come through.  This experiment will work best if you time it so that the sun is shining into the window, so if your window faces east, do it in the morning.  If your window faces west, wait until afternoon.  If your window faces north or south, you may have to move to a different room.  Darken the room and you should be able to see the beam of sunlight, with dust particles floating in it.  This in itself is a wonderful experiment, just watching all of the "stuff" that is in the air you breath. 
     
     Once you are through watching the dust, hold your hand in the beam of light.  Now, gently scratch the back of your hand, as if it itched.   Watch as you scratch your hand and you will see LOTS of particles being scratched off your hand.  Those particles are dead skin cells.  Every time you scratch, wash, rub, etc., these dead cells fall off.  
     
     Most of my references say that as much as 80% of the dust on your furniture is made of dead skin. Don't worry about all that dead skin going to waste.  Your house is also full of tiny creatures called dust mites.  The dust mites eat dead skin cells.  They are too small to see without a powerful microscope, but they are everywhere in your house.  Opps.  Now I have given you a reason to itch.  These dust mites are the real cause of most dust allergies.  Their droppings and broken up pieces of their exoskeleton float through the air as dust.  That is what causes your allergic reaction.  Isn't it nice to know about some of the things that are in the air you breath?

This experiment  was re-printed with permission from Robert Krampf