We have seen that humor and laughter positively influence our body in many ways, but little research has been done on whether a better sense of humor actually helps keep you from getting sick. However, since people with a better sense of humor have higher IgA levels, and since research has shown that those with higher levels of salivary  IgA are less likely to get colds or be infected with Streptococcus, humor should reduce the frequency of colds. The only study to directly examine this question found that the impact of one's sense of humor upon colds depends on the kind of sense of humor you have. It was only individuals whose sense of humor took the form of seeking out and appreciating humor who had fewer and less severe colds/flu than their low humor counterparts. Surprisingly, those whose sense of humor took the form of initiating humor more often did not have fewer or less severe colds/flu. The researchers argued that being a person who likes to tell jokes or otherwise initiate humor takes them into more frequent contact with other people, which serves to expose them to infectious agents more often, robbing them of the advantage that a more active sense of humor otherwise offers. Obviously, more research is required to clear up this confusing picture. The importance of active use of one's sense of humor in producing humor's health benefits was confirmed in another study in an unusual way. It found that among a group of mothers with newborn infants, those who actively used humor to cope with the stress in their lives had fewer upper respiratory infections and their infants also had fewer infections. This seemed to be because these mothers had higher levels of immunoglobulin A (A) in their breast milk. Among adults, if we look at bodily symptoms alone, independent of any diagnosed illness, there is some evidence that individuals who have more negative reactions to humor report more bodily symptoms and complaints. Students complaining of cardiovascular  symptoms and gastroenterological   symptoms also have been shown to have this more negative reaction to humor. Why do newborn infants whose mothers use humor to deal with stress have fewer infections?
Because they don't often get upper respiratory infections. Because they are stronger since they were born. Possibly because of the higher levels of immunoglobulin A in their breast milk. Because their mothers take better care of them.