Sneezing is more likely to be due to an upper respiratory problem or infection. Keep a close eye on them, sometimes stress from moving to a new home for example can bring out symptoms such as sneezing, wheezing or rattling chests due to an underlying infection.
This time of year, when warm and dry can cause dusty conditions, these may cause sneezing so check bedding and ventilation is adequate.
I also use a dust extracted product as bedding such as easibed or Rapport, and am careful to check on how much dust is in the sheds, it is surprising how quickly dust can build up!
Here is some useful information on respiratory problems..
http://poultrykeeper.com/poultry-diseases-and-disorders.html