A study conducted at the University College London Institute of Cognitive Neuroscience has shown that a build-up of the stress hormone cortisol can be measured from the oily secretions around your ear canal.

This could open the door to better ways of diagnosing psychiatric conditions including depression, according to lead author Dr Andres Herane-Vives who wants to understand what raised or lowered levels of cortisol might indicate. He has also developed a new type of swab which won’t damage the eardrum.  Cortisol is known as your “fight or flight” hormone. When it sends out alarm signals to the brain in response to stress, it can influence almost every system in the body, from the immune system to digestion and sleep.
Source : BBC