Here you are enjoying beautiful music at the orchestra concert and suddenly you get urge to cough. It usually happens when you are recovering from a cold. It can be disturbing for someone who performs so it is better to be prepared. Bring some cough medicine or unwrapped candy or lozenges with you. Yes, unwrapped because they can make noise as well. Keeping quite even for the people that surround you in the auditorium is also important. They all paid for the tickets and want to enjoy the concert. You can also try to hold and cough during the loud passages of music. Now, if all the above do not work, then you can excuse yourself and quietly exit the concert hall. You may not be able to re-enter the concert hall immediately after you stopped coughing. Ushers will let you know preferred re-entrance to the auditorium.
Hopefully this hint will be handy one day, especially if you are not a regular when comes to concerts.
Another great tip for the orchestra concert is when to clap. Usually audiences tend to clap when the piece is finished. This gesture of holding the applause between the movements is actually considered respectful. Applause can easily break the performer's concentration. The conductor will usually let the audience know when the piece is completed by putting his/her baton down and turning towards the audience.
You also may want to remember this proper concert etiquette - no talking, tapping, humming, turning program pages, standing or leaning forward in the seat, and of course unwrapping candies or your cough lozenges. Such things my disturb both sides, audiences and performers.