Firina

Our 2015 Tiguan has developed a very strong smell that I can only describe as peroxide bleach, inside the car within the last week. It is there all the time and so strong it is causing irritant to the throat etc. I have taken it to our mechanic today but he is unable to find the source. He says there are no leaks etc to be found and is perplexed. Does anyone have any suggestions what this might be( our mechanic has been in business for many years & never come across this before).