Sneezing timidly may be hazardous to your health. Air escaping from the nose and mouth during a sneeze can reach speeds of up to 160km/h. Sneezing while trying to hold your breath, sealing your lips or pinching your nose creates enormous pressure in the nose and throat.
According to a US ear, nose and throat specialist, the pressure may force bacteria from your nose into your sinuses or into your ears through the eustachian tubes. The best thing to do is to cover your nose and mouth with a tissue and go for it.
There have also been cases of severe physical damage caused by sneezing. Some years ago there was a report of a man reading a newspaper and, feeling he was about to sneeze, turned his head to the side and sneezed. The result was his neck, already at the limit of its ability to turn, being forced further and snapping. The gentleman is reported to now be a paraplegic.
Whether these are true, rumours, or folklore, sneezing is definitely a hazardous bodily function.