Many Japanese uses face mask everyday. Surprising that so commonly used that, even oversea visitors first thought that they do so to protect themselves from pollution, which we were very wrong.
The main reason for using mask is hygiene. The Japanese character is respectful and considerate of others, so if you caught a flu or cold, you do not want to spread it to others. Besides the usual seasonal cold in times of winter, it is also frequently used during spring to protect themselves from pollen allergies.
But some Japanese friends have told me that there are other reasons. Many of them like to wear a mask for the simple fact of preserving their privacy, a way to put a barrier to others, to go unnoticed and thus feel calmer. Unfortunately this type of use is increasing among young people.
The most common mask is white, but also can find countless designs, and even different types of aroma.