Allergies..... plain and simple.  Allergies (such as pollen) happen because your body's immune system is overreacting to antigens that are not harmful to the human body.  Without going into detail, simply speaking, if we were "intelligently designed" why would our creator create our immune system so flawed?  Our immune system is designed to detect antigens or foreign objects in our body that could harm us.  This is why bacteria and other pathogens go to great lengths (through our own immune system acting as selective pressures) to change their surface antigens (proteins that our immune system recognizes) so that our immune system cannot recognize them and destroy them.  So.. it would seem very unintelligent for our immune system to overreact to harmless foreign objects such as pollen. Not very "intelligent".

I suffer from spring allergies and let me tell you there is nothing intelligent about my body over reacting to harmless antigens. It just goes to show that our immune system reacts "unintelligently" to foreign objecs not payin attention to whether they are harmful or not and in fact reacts in a manner that is more harmful than good to things that cannot hurt us.  This is not intelligent design but simply chemistry and physics.  An intelligent designer would obviously not build a human body that is flawed with allergies.  One of the many examples on how the theory of intelligent design is a flat out lie.  Our bodies are not "intelligently designed" because if they were, they would not hurt us due to other "intelligently designed" things such as pollen.