I am constantly sneezing everyday what is the reason for this? and ways to prevent it?

Allergy: You have to find the cause of the problem before a treatment can be recommended.

Allergies likely.: Persistent sneezing in the warmer months, could be a sign of seasonal allergies. It could be indoor or outdoor allergies. Pets often contribute to this. Seasonal and perennial Rhinitis are both possible diagnosis. Consult your doctor for management. OTC allergy meds like Loratadine or Cetirizine may may be tried on a once a day basis.