Why Is Dust Regarded As Unwanted?

House dust can be a health hazard !  It can trigger allergies as well as aggravating some respitory conditions such as asthma.  Dust is pretty undesirable because it contains a lot of dead cells from our skin, dust mites which live on the cells, the droppings that these mites make and microscopic particles of pollen, minerals bacterial spores and mould.
So, if we have enough dust in the home, then it is obviously going to affect the quality of the air that we breathe and so it is best to get rid of it.
In addition, dust may contain some toxic substances from the external environment such as lead or even asbestos fibres.  
When dusting it is important to use a slightly damp cloth so that the dust sticks to the cloth, rather than just being moved elsewhere.  You should also make sure that you keep rooms well aired, to minimise dust build up.