Physical exertion, such as practicing sports, may have an influence on the secretion and composition of saliva. As a result of intensive physical exertion, the saliva immunoglobulin concentration decreases and the concentration of protein – the output of protein (mg/min), however, remains constant – and the viscosity of the saliva increase, while the watery secretion decreases. Moreover, saliva testosterone levels decrease and salivary cortisol levels increase. The saliva Na+, K+, Ca2+ and PO43- concentrations increase slightly or remain unchanged. After a single physical exertion, the alterations are reversible and the values return to baseline within a few hours. In the case of long lasting intensive physical exertions, for instance lasting several months, particularly the decrease in the concentration of the most prevalent immunoglobulins in saliva (s-IgA) seems to have a more permanent character. This has a detrimental effect on the immunological defence, which may reduce oral as well as upper respiratory tract health. Complaints about this are not uncommon among serious athletes who are active at a high competitive level. Among these athletes, the combination of changes in the composition and secretion of saliva, together with intense mouth-breathing and an adjusted diet and drinking habits carry a higher risk of developing caries and erosion. However, in case of decent oral health selfcare, the detrimental effects on oral health can be prevented.