There are bitter taste receptors lining the smooth muscle that surrounds airway passages   that lead to the lungs.  These are the same receptors found on the tongue.  It is well known that the ability to taste bitter has evolutionary benefits.  For example, bitter tasting toxins can be detected in foods, and thereby avoided or at least regulated; meaning you won’t eat too much of something that tastes really bad!

Interestingly enough, inhalable toxins can be detected in airways, just like they would be on the tongue. The airway response to detection is what’s most interesting.  One school of thought is that logically, when bitter toxins are detected in the lungs, the airways will close.  This prevents the toxin from entering the lungs, makes breathing difficult, and inevitably forces the individual to leave an unhealthy environment.

What has been observed though, is quite the opposite.  In mice, inhaled quinine (a bitter compound) caused the airways to relax, instead of constrict! In fact, quinine worked better than albuterol (a drug commonly used to treat asthma) at relaxing airways. There must be a benefit to having such a reaction.  It has been proposed that opening airways may reduce the risk of infection or aid in clearing infection when toxins are inhaled, but it is still unclear.  What is clear, is there will likely be new asthma medications developed in response to this interesting genetic trait!