sneezing is used for getting rid of bacteria / viruses by the body & the immune system gets rid of bacteria / viruses once they have invaded the body ->  sneezing is used by the immune system to get rid of bacteria and viruses in the body  sneezing is used by the immune system to get rid of bacteria and viruses in the body & if a process is used by something then that something causes that process -> sneezing is caused by the immune system