Mostly it is due to allergies. Allergic reactions are the immune system’s response to perceived invaders in the body such as mold, dust and sometime people have some sensitivity to light that can trigger a sneeze.
Bulid up your immunity: First try to identify the source. Second, once the sources are discovered, they should be avoided. Third, and most important, general health and resistance should be built up to establish immunity to them.
Squeez half a lime in a glass of lukewarm water, add one teaspoon of honey. Take daily first thing in the morning for several months. This remedy not only flushes the system of toxins but also acts as and anti allergic agent.