Another less common verbal response in the United States and Canada to anothers sneeze is "Gesundheit", which is a German word that means, appropriately, "good health". Several hypotheses exist for why the custom arose of saying "bless you" or "God bless you" in the context of sneezing:

Some say it came into use during the plague pandemics of the 14th century. Blessing the individual after showing such a symptom was thought to prevent possible impending death due to the lethal disease. In Renaissance times, a superstition was formed claiming ones heart stopped for a very brief moment during the sneeze; saying bless you was a sign of prayer that the heart would not fail. It has also been stated that one says "(God) bless you" so that one does not catch the flu, cold, or any other forms of sickness.Other cultures have similar traditions:

In China, after a person sneezes they often say "百岁!" which translates to "may you live one hundred years!" the pronunciation is similar to "bless you" in English. pronunciation: [Bai Sui]
In Iran, it is common to respond to sneezing with the Persian phrase عافیت باشه âfiyat bâše, which translates to "health", similar to common European expressions. Indian culture is to respond with Krishna, similar to a blessing in western cultures. In Italy after a person sneezes the people present respond with the word "salute" (meaning: health). The louder the sneeze the more emphatic the response. In Slovakia, after a person sneezes, it is proper to say "Na zdravie!" which means "For health!
Culture
In Indian culture, especially in northern parts of India, Bengali (Bangladesh and Bengal of India) culture and also in Iran, it has been a common superstition that a sneeze taking place before the start of any work was a sign of impending bad interruption. It was thus customary to pause in order to drink water or break any work rhythm before resuming the job at hand in order to prevent any misfortune from occurring. Contrarily, in Polish culture, especially in the Kresy Wschodnie borderlands, a popular belief persists that sneezes may be an inauspicious sign that, depending on the local version, either someone unspecified or ones mother-in-law speaks ill of the person sneezing at that moment. In other regions, however, this superstition concerns hiccups rather than sneezing. As with other Catholic countries, such as Mexico, Italy, or Ireland, the remnants of pagan culture are fostered in Polish peasant idiosyncratic superstitions. The practice among Islamic culture, in turn, has largely been based on various prophetic traditions and the teachings of the prophet Muhammad. An example of this is Al-Bukhaaris narrations from Abu Hurayrah that Muhammad once said:
When one of you sneezes, let him say, "Al-hamdu-Lillah" (Praise be to God), and let his brother or companion say to him, "Yarhamuk Allah" (May God have mercy on you). If he says, "Yarhamuk-Allah", then let [the sneezer] say, "Yahdeekum Allah wa yuslihu baalakum" (May God guide you and rectify your condition). Verbal responses
In English-speaking countries, one common verbal response to another persons sneeze is "[May God] bless you".