Recurrent aphthous ulcers are the most common ulcerative damage in the oral mucosa. The prevalence in the population is about 10 to 30%. It is characterized by periodic recurrent episodes with varying intervals, ranging from short continuous episodes with one episode to long intervals of 2 to 3 months. The ulcers tend to occur on the lips, tongue and cheeks, but also on the floor of the mouth, soft palate and pharynx. The etiology of recurrent aphthous ulcers is not fully understood and is complex, and may be related to some predisposing factors. There are many common clinical triggers, such as mental stress, indigestion, constipation, intestinal parasites, sleep deprivation, fatigue, menstrual cycle and menopause. Mouth ulcers are the most common oral mucosal disease and are deeply distressing because of their pronounced burning pain. Its main pathogenic factors include immune factors, genetic factors, systemic disease factors, environmental factors and other factors. Recurrent aphthous ulcers are not infectious and therefore not contagious. Since recurrent aphthous ulcers have a genetic predisposition, they can show family aggregation, and children with a father or mother with recurrent aphthous ulcers can also have recurrent mouth ulcers. This is not contagious and is mainly related to genetic factors.