Due to the COVID-19 pandemic, the use of face masks has increased, resulting in potential health-related side-effects. Therefore, the study aimed to analyse the effect of wearing face masks on self-perceived dry mouth and halitosis. A questionnaire addressing the daily wearing time of different face masks (community masks, surgical/medical masks and KN95-/N95-/FFP2-masks) and self-perceived dry mouth and halitosis was given to adults attending or working at a university hospital. Statistical analysis was performed using Wilcoxon signed-rank test and multiple linear regression analysis (p < 0.05). 3750 participants (age: 50.4 ± 15.5 years; 60.0% female) were included. During the pandemic, face masks were used for 4.7 ± 3.8 h per day: community masks: 0.9 ± 2.0 h, medical/surgical masks: 1.9 ± 2.8 h and KN95-/N95-/FFP2-masks: 1.9 ± 2.5 h per day. The use of face masks significantly increased self-perceived dry mouth and halitosis (both p < 0.001). Self-perceived dry mouth and halitosis increased with increasing wearing time (community masks: dry mouth: p < 0.001, halitosis: p = 0.014; medical/surgical masks: both: p < 0.001; KN95-/N95-/FFP2-masks: dry mouth: p < 0.001, halitosis: p = 0.011). The perception of dry mouth and halitosis was increased in females compared to males (both: p < 0.001). Participants used to wearing face masks prior to the pandemic perceived dry mouth to a higher extent (p = 0.043). Self-perceived halitosis was lower in older than in younger participants (p < 0.001). Due to the increased perception of dry mouth and halitosis, people might abstain from wearing face masks. Further studies need to analyse measurable changes in dry mouth or halitosis.